Misconception: They used to be Elves
The article states:
According to Tolkien, at least some of the orcs used to be elves.
That's right, some orcs have the same ancestors as the beautiful
Legolas. Apparently they were tortured and that's how they changed
both their appearance and their personalities to the gross and evil
kind. They, like elves, can die in battle, but viewers never spend
enough time with them to see if, at least some orcs, still possess
the immortality of their elf ancestors. Despite the explanations,
it's hard to believe that torture can create an entirely new
species, bot just a new attitude or outlook.
It's more like that was one of the possible victims that were
captured and tortured. In The Silmarillion this is indeed the case.
However there were different ideas as far as their origin and elf was
only one possible source. I think it was in Unfinished Tales that this I
transcribed but again this doesn't really matter where:
To the unfriendly who, not knowing them well, declared Morgoth
must have bred the Orcs from such a stock the Eldar answered:
'Doubtless Morgoth, since he can make no living thing, bred Orcs
from various kinds of Men, but the Drúedain must have escaped his
Shadow; for their laughter and the laughter of Orcs are as different
as is the light of Aman from the darkness of Angband.' But some
thought, nonetheless, that there had been a remote kinship, which
for their special enmity. Orcs and Drûgs (Drúedain) regarded the
other as renegades. [Author's note.] - In The Silmarillion the Orcs
are said to have been bred by Melkor from captured Elves in the
beginning of their days; but this was only one of several diverse
speculations on the origin of the Orcs. It may be noted that in The
Return of the King V 5 the laughter of Ghân-buri-Ghân is described
'At that old Ghân made a curious gurgling noise, and it seemed that
he was laughing.' He is described also as having a scanty beard: it
'straggled on his lumpy chin like dry moss' and dark eyes that
showed nothing.
Note the term 'Púkel-men' (a translation: it represents
Anglo-Saxon púcel 'goblin, demon', a relative of the word 'púca'
from which Puck is derived) was only used in Rohan of the images of
the Dunharrow.
Also Treebeard says that the orcs were mockeries of elves just like
trolls were mockeries of Ents. This does not suggest they were elves but
yes some of them were thought to be nonetheless.
As for a new species: that's not the right word. The word is 'race'.
Now whether they were a race or not is another matter entirely but
Tolkien wrote quite a bit on creation versus making and I don't see that
this will be improved by touching on that.
As for whether they were immortal like the elves (which doesn't mean
they couldn't die) it's true we do not really know that; I cannot think
of seeing anything about it though that doesn't mean I haven't seen it.
It probably was inconsequential to Tolkien and left to the imagination.
I would say that they probably were not but that's just a guess. Of
course immortal doesn't mean that they would be returned to life: Fëanor
was not for example. Eru Ilúvatar judged him directly for all the evils
he did. Unlike Glorfindel who was resurrected after his fall with one of
the Balrogs in the Fall of Gondolin.