Putting aside the fact that we are not bound to follow Tolkien's definition of the orcs (if we stand on the shoulders of giants, it's so we can reach higher than they did), especially when Tolkien's own definition in life evolved...
...this explanation of Tolkien's orcs is contradicted by Tolkien's own words and actions at just about every level.
Evil, they may be, but mindless is in every way at odds with what's on the page. They are noted in the Hobbit (yes, the Hobbit says goblin, but Tolkien was very explicit that Goblins and orcs are synonymous in his works) to be technologically adept and creators of many devices that have since troubled the world. They also display an aptitude for strategy and cunning in warfare, and a degree of loyalty to other members of their "clan" (eg, Grishnak returning to Ugluk's troops because of the good lads he left behind), plus a desire for independence from Sauron and his army (Gorbag and Shagrat discuss striking out on their own after the war is over also in TTT).
In LOTR, the Isengard-style industrial spoliage of the Shire is explicitly refered to as ORC-works, too. Not Saruman-work.
Some who aren't bothering to read the foreword, were Tolkien explicitly respond to the notion of the Lord of the Rings as an analogy, and specifically a WW2 allegory with a lengthy answer that boils down to "Oh heck no."
Beyond Tolkien's explicit statement, there's also the fact that he was vehement during the war about how the germans shouldn't be dehumanized (because no one has the right to dehumanize another people; not the germans to other people and not other people to the germans), so the idea that he wrote a dehumanizing take on them, reducing them to footsoliders of evil, would be...strange.
Finally, the *chronology* doesn't work. At all. The Hobbit, introducing the Goblins (again, synonymous with orcs to Tolkien) and the Necromancer (Sauron), was largely finished writing in 1932. Some of the elven stories (featuring Dark Lords, evil orcs and all that jazz) predates even that - some of them were written one whole world war earlier. All of which is...before Adolf Hitler even rose to power, let alone before there were even the first hints of a second world war.
This isn't to say the War didn't have some influence on the writing (although Tolkien's experience in the First one had a lot more influence). But this isn't it.
(Oh, and in answer to the race-species debate: no, elves, hobbits and probably orcs are not species, at least not in Tolkien. Tolkien explicitly acknowledged in his letters that biologically, human and elves are in fact the same (that whole "reproducing and having fertile offspring" thing). And he also explicitly wrote Hobbits are even closer to humans than elves are, so all three, at least, are one biological species. Orcs may or may not be corrupted elves or men, in which case they'd definitely be the same biological species; and even if not, are still apparently capable of some form of interbreeding with humans so either same species or a very close relative)