One thing I'd suggest for Middle Earth with DR is using extra models per orc unit to give them a more hordish feel (if you have the figures!). So you might have your uruks of Mordor in units of 18 or 24, even though they'd only have 12 Strength Points - just for the aesthetics.
I'd go with something like this:
Isengard
Uruk-hai = Bellicose Foot (in outsized units as above). There's no exact fit for the Isengarders, but Bellicose Foot at least gives them the speed that Tolkien mentions ("trained to move at great speed for long distances") through Move 8" and Fleet Footed. I'd factor in their shooting as immediately preceding their charge/counter-charge and helping its impact).
Warg riders = Lesser War Beasts (with or without Flame Attack to represent mounted archers)
Dunlendings = Light Foot (wall of spears covers the pikes mentioned at the Isen)
Dunlending horsemen = Heavy Riders (or Light Riders - we don't get much info about them)
Half-orcs = Offensive Heavy Foot (or possibly even Elite Foot): "Ferocious, mail-clad, and armed with axes). Potent enough to cut through to Theodred and cut him down.
Moria/Misty Mountains
Lesser orcs (the bulk of the force) = Light Foot with Mixed Weapons and Fearful. Outsize units where possible
Uruks (a minority - but present in Moria and presumably constituting Bolg's bodyguard) = Bellicose Foot as for Isengard.
Wargs and Warg riders = Lesser War beasts (again, with or without Flame Attack for mounted archers)
Bats = Ravenous Hordes with Flying (breaks the rules, but I think that's the best way to represent them if you count them as a troop type at all).
Trolls (in Moria) = Elite Foot in Reduced Model Units (one, two or three) with Mystical Armour and maybe Venomous.
Mordor
Uruks = Bellicose Foot in outsize units (as above). The mainstay of the armies of Mordor.
Lesser Orcs = Light Foot with Mixed Weapons and Fearful. Outsize units where possible. Probably only in action in great numbers at the Cormallen Field when Sauron emptied Mordor.
Haradrim = Light Foot
Haradrim Cavalry = Light and Heavy Riders
Easterlings = Offensive Light Foot
Variags of Khand = Offensive Heavy Foot (or Elite Foot, perhaps)
Mumakil = Greater War Beasts
Trolls = Elite Foot in Reduced Model Units (one, two or three) with Mystical Armour and maybe Venomous.