Snaga=slaves=applied to any Orc by a stronger one.
Uruks=black uruks of Mordor=Uruk hai=strongest breed of orcs.
Half orcs=goblin men=part orc,part man.
Thats it no more orcs,everything else is just made up troop types which helps with variety in the game but in terms of real background they are all from these types just different training,equipment and different levels of influence from their masters.
For the sake of completeness :Tolkien puts forward various ideas about the ""olog-hai trolls" one of which is that they are giant Orcs.
Boldogs are Maiar that have taken the form of "mega orc leaders" and as such are the most powerfull "Orc" of all and in game terms would be somewhere between a Balrog andRadagast.