Everyone is likely to have a different answer for you on this one. Some people mix uro species and some people mix whole reptile species (uros and desert igs, for example). Some folks don't keep more than one critter per cage.
Personally, I would not mix uro species. No possibility of cross-breeding, which some people are *trying* to do, but I don't feel is a good thing. Also, different species are different species, even if they are all uros - there could be stress and domination problems that we don't recognize or understand.
BUT...
Doug Dix mentioned to me about a year ago when chatting at a reptile show that the species more closely related (Malis, Nigers (Saharans), and Moroccans) can usually co-exist.
So take what you will from this. 
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Torey
Salem, Oregon, USA
1.1 Uromastyx Geyri (Joe and Arthur)
2.0.1 Uromastyx Dispar Maliensis (Tank, Turtle, and new neighbor Spike)
1.2 Anolis Carolinensis (Bowser, Leeloo, and Sprocket)
1.1 African Dwarf Frogs (Bruce and Sheila)
1.0 Betta Splendens (Mr. Miagi)
1.1 Felis Domesticus (Roscolux and Jenny)
And several miscellaneous community fish
