[skip spence]

I think it is a mistake to see Orcs as a distinct race who are separated from Elves and Men by how they look (ie fangs, long ape-like arms, crooked legs). What constitutes an Orc is rather how it acts IMO although they of course also had many physical characteristics that stood out. Orcs are a representation of all that is bad with mankind. They do nothing that Men haven't done a million times throughout history.

Therefore I think it is difficult to accurately separate the different categories of orcs from each other. The difference between Uruk-Hai, Snaga, Orc-men and even Elves and Men is not clear cut. Just the fact that Men (and Elves in all likelyhood) are interbreedable with Orcs suggest that biologically they are all members of the same species.

If Orcs were some kind of grotesque monsters it's hard to imagine Orc-men blending into human societies. Consider also how the Elves, when they first came face to face with the Orcs in Beleriand, thought them to be Avari gone wild. They clearly recognised them as being kin, albeit cruel and wicked.