In the Secondary World of Middle-earth, there exist, in addition to men, at least seven species capable of speech and therefore of moral choice--Elves, Dwarves, Hobbits, Wizards, Ents, Trolls, Orcs. Of these, dwarves, hobbits, wizards, and ents are like us in that each individual is both good and evil: one may resist temptation more successfully than another, but even the best may fall, and even the worst may repent.

[skipping here Auden's view of elves - irrelevant to this discussion and possibly a bit distracting to a forum that has had access to The Silmarillion (aka Elves Behaving Badly) when Auden had not]…

Unlike us, too, are the Trolls of Mordor and the Orcs, for they appear to be irredeemably evil and incapable of repentance: on meeting either, there is only one thing to do: kill. I must confess I am not quite happy about these beings, for their existence seems to imply that it is possible for a species that can speak, and, therefore, make moral choices, to be evil by nature. I can readily believe that Sauron, by cross-breeding and training of creatures already in existence, can produce the pterodactyl-like creatures ridden by the Nazgul, for these are "dumb" animals, who can be used for evil purposes but cannot be called evil in themselves. I am not so ready to believe that the Orcs were bred by Morgoth and the Mordor Trolls by Sauron, for neither are simply animals. If Evil can not only seduce the good but also create beings who are evil from the beginning, then one cannot, as Tolkien does, call God "The One"; there must, in that case, be Two, a good One and an evil One.

And I have a moral, as well as a theological, objection. In the Primary World we are all aware of our deplorable tendency, when our interests, still more the interests of our social group, come into conflict with others, to identify our cause with Good and that of our enemies with Evil. There have been Just Wars: most of us would agree that it was as morally necessary for England [sic] and the United States to resist Germany and Japan by force of arms as it was for Rohan and Gondor to resist the armies of Saruman and Sauron. Individual men can be wicked: Hitler was not another Sauron, but he seems to have come as close to being one as is possible for a mortal. It would, however, be grossly unjust to say that all Germans and Japanese, even the majority, were wicked.

Even in a Secondary World, I feel that irredeemable wickedness should be ascribed only to individuals who are nameable or countable— Sauron, the Lieutenant of Barad-dur, the nine Nazgul--not to anonymous crowds. When it comes to the men who fought on Sauron's side, I am happy to see that Tolkien recognises this. If we knew more about the historical reasons for the enmity between Gondor and the Haradrim or the Easterlings, we can be certain we should find that Gondor was not completely innocent. Consequently, reconciliation is possible; Aragorn can pardon and make peace with them.

Auden, W. H. (1967) "Good and Evil in The Lord of the Rings," Tolkien Journal: Vol. 3: Iss. 1, Article 1. Available at: https://dc.swosu.edu/tolkien_journal/vol3/iss1/1

“With regard to The Lord of the Rings, I cannot claim to be a sufficient theologian to say whether my notion of orcs is heretical or not. I don’t feel under any obligation to make my story fit with formalized Christian theology, though I actually intended it to be consonant with Christian thought and belief, which is asserted somewhere, Book Five, page 190, where Frodo asserts that the orcs are not evil in origin. We believe that, I suppose, of all human kinds and sorts and breeds, though some appear, both as individuals and groups to be, by us at any rate, unredeemable. . . . .”

Unlike us, too, are the Trolls of Mordor and the Orcs, for they appear to be irredeemably evil and incapable of repentance: on meeting either, there is only one thing to do: kill.

Can you remember or find a citation? I don't recall any orc prisoners in LOTR, and obviously Auden missed it too if you are right. Nor do I remember kindly treated orc captives TH (where they would be called 'goblins' I suppose, and might or might not be the same as orcs: another contentious area of fandom!)
So I may have missed something, or maybe you are thinking of Tolkien-themed entertainments written later, by others - the secondary secondary world, as it were.
It is easy to misremember where one read/saw something!

There could be a very interesting study of how people writing fan-fiction, games, movies, TV etc. had interpreted or adapted orcs; and whether that had changed over time; and whether any changes related to changes in society etc.

But goodness knows I wrote enough just sticking to LOTR, so such a study would be well beyond me.

Then the elves put things on him [Thorin] and shut him in one of the inmost caves with strong wooden doors, and left him. They gave him food and drink, plenty of both, if not very fine; for Wood-elves were not goblins, and were reasonably well-behaved even to their worst enemies, when they captured them. The giant spiders were the only living things that they had no mercy upon.

Captives must not be tormented, not even to discover information for the defence of the homes of Elves and Men. If any Orcs surrendered and asked for mercy, they must be granted it, even at a cost.* This was the teaching of the Wise, though in the horror of the War it was not always heeded.

*[footnote to the text] Few Orcs ever did so in the Elder Days, and at no time would any Orc treat with any Elf. For one thing Morgoth had achieved was to convince the Orcs beyond refutation that the Elves were crueller than themselves, taking captives only for 'amusement', or to eat them (as the Orcs would do at need).

Probably from Italian orco (“man-eating giant”); later revived by J. R. R. Tolkien, partly after Old English orc, which he took to mean "demon". Both are from Latin Orcus (“the underworld; the god Pluto”)

Thither came the sons of Men to hear their doom, and thither are they brought by all the multitude of ills that Melko's evil music set within the world. Slaughters and fires, hungers and mishaps, diseases and blows dealt in the dark, cruelty and bitter cold and anguish and their own folly bring them here; and Fui [Nienna] reads their hearts. Some then she keeps in Mandos beneath the mountains and some she drives forth beyond the hills and Melko seizes them and bears them to Angamandi, or the Hells of Iron, where they have evil days. Some too, and these are the many, she sends aboard the black ship Mornië, who lieth ever and anon in a dark harbour of the North awaiting those times when the sad pomp winds to the beach down slow rugged paths from Mandos.

Edith Hamilton suggested that the asphodel of these fields are not exactly like the asphodel of our world, but are "presumably strange, pallid, ghostly flowers."

A different proposal explains the name of the land as 'field of ashes' basing it on sphodelos or spodelos, an alternative version of the name

Only mortals related to the gods and other heroes could be admitted past the river Styx. Later, the conception of who could enter was expanded to include those chosen by the gods, the righteous, and the heroic.

The Elysian Fields were, according to Homer, located on the western edge of the Earth by the stream of Okeanos