Continuing from an argument presented in:
It seems that it is not a case of orcs being inevitably damned - qua orc (they are not born-into a state of damnation - that could never happen in a world created by a good God); but a matter of orcs never, as a matter of fact, repenting their sins.
It is as if their nature and training and circumstances combine such that orcs will never admit to themselves (or to God) that they have erred or sinned; they are never humble; they are motivated (and controlled) by negative emotions such as pride, hatred, greed, idleness, fear...
Such people exist. But with people we can never be 100 percent sure (as we are with orcs) that one of them, one day, may not take what seems the very simple step of fully acknowledging their own defects.
But the difference between orc-like people and actual orcs is 'merely' a matter of hostorical probabilities - the likelihood of repentance being, say 0.1% for the most evil man, and zero percent for an orc.
In practice there are plenty of people who could repent, but don't - don't get anywhere near repenting no matter what happens to them. They always blame others for everything; always see themselves as the victim.
Orcs are simply these people taken to the limit.
How does this happen? Because first Morgoth, then Sauron, create societies of inverted virtue; where evil is the good, ugliness is a positive, lies are approved, virtue is punished - and orcs are brought-up in such a depraved society so they know nothing else.
In other words, pretty much the same as modern Men under political correctness, or Communism - except these are not (yet) so overwhelmingly, monolithically inverted as the societies of Morgoth or Sauron.
So what would happen if an orc was born and raised among good men, elves or hobbits? I predict he would be like a bad man, elf or hobbit - that is to say he would (due to his inbred, ruined nature) be as bad as a bad man, elf or hobbit - but not necessarily any worse.
Would he be capable of repentance? Maybe - in fact yes! At least as capable as a bad man, elf or hobbit. Which is to say: very unlikely, but not impossible.