It's to my understanding that orcs were once elves that were captured and tortured by Morgoth ages ago, becoming what's now orcs. Being captured and tortured is obviously not their fault, therefore are they considered evil by Eru and the Valar? Will they be treated differently compared to men and elves when they die?
Tolkien's final thoughts on Orcs are contained in the "Orcs" essays in Myths Transformed, published in History of Middle-earth 10: Morgoth's Ring. There are several passages there that have bearing on this question, but — as may be expected — the question of what exactly the origin of Orcs is will also influence the answer.
One discussion in these texts explores the possibility of Orcs being ultimately redeemable:
But Men had not yet appeared, when the Orcs already existed. Aulë constructed the Dwarves out of his memory of the Music; but Eru would not sanction the work of Melkor so as to allow the independence of the Orcs. (Not unless Orcs were ultimately remediable, or could be amended and 'saved'?)
Another part of the same text explores the possibility of Orcs as being originally some kind of spirit-being, such as lesser Maiar:
...they would become more and more earthbound, unable to return to spirit-state (even demon-form), until released by death (killing), and they would dwindle in force. When released they would, of course, like Sauron, be 'damned': i.e. reduced to impotence, infinitely recessive: still hating but unable more and more to make it effective physically (or would not a very dwindled dead Orc-state be a poltergeist?)
A third part discusses the fate of Orcs-as-Elves:
It remains therefore terribly possible there was an Elvish strain in the Orcs. These may then even have been mated with beasts (sterile!) — and later Men. Their life-span would be diminished. And dying they would go to Mandos and be held in prison till the End.
And a fourth puts forward the theory that Orcs were parts of Melkor/Morgoth's distributed spirit (in which case they'll share the same fate as him):
It will there be seen that the wills of Orcs and Balrogs etc. are part of Melkor's power 'dispersed'.
A further and later text, where Tolkien provides support for the theory of Orcs-as-Men also mentions a fate for them:
But even before this wickedness of Morgoth was suspected the Wise in the Elder Days taught always that the Orcs were not 'made' by Melkor, and therefore were not in their origin evil. They might have become irredeemable (at least by Elves and Men), but they remained within the Law.
So ultimately the question of whether or not they can be redeemed depends on their origin.
Since you ask with specific reference to the origin given in the published Silmarillion, the answer is given in the third quotation above: they are held in Mandos until the End, but Tolkien does not speculate on what may happen to them after.
It's notable that being held in Mandos until the End is the same fate as that given for evil-doing Elves in the essay entitled "Of re-birth and other dooms of those that go to Mandos" (part of Laws and Customs among the Eldar, also published in Morgoth's Ring):
The Shadow upon Arda caused not only misfortune and injury to the body. It could corrupt the mind; and those among the Eldar who were darkened in spirit did unnatural deeds, and were capable of hatred and malice. Not all who died suffered innocently [...] Of the others, the wrong-doers, many were held long in 'waiting', and some were not permitted to take up their lives again.
The answer is therefore clear: within the scope of your question (Orcs-as-Elves) they are considered evil by the Valar, and have the same fate as evil-doing Elves, but Tolkien doesn't speculate as to their fate beyond the end of the world (nor does he do so for Elves), which leaves the question of how Ilúvatar views them open. For other origins, they may or may not have different fates.