It requires a lot of research and consideration to properly house different species in the same cage. For one, the cage should be much larger than a cage would need to be for an individual of either species, second, the husbandry requirements should be very similar for both species. The animals themselves would need to be able to tolerate other species in their 'territories' or have little actual contact with each other. Or have different activity times or 'levels' thus contact is minimized. It is also good if both species have different diets as well.
Then of course, there are the problems that could arise as described by the other posters who responded to your question.
Uros require much higher temps than bearded dragons. Depending on the species of Uromastyx, can get about the same size or much bigger (ie Egyptian Uromastyx). Both bearded dragons and uro's eat mostly vegetation (adult dragons eat about 90% of their diet in vegetation, Uros are 100% vegetarian though some species may add a bit of insect 'meat' into their diets but compared to dragons, this is a very low percentage). Uros require much higher basking temperatures and I believe, ambient temperatures than dragons. This presents a difficulty in ensuring both animals are housed comfortably. One thing both have in common though, is neither requires a high humidity.
In a large enough cage, a better choice of cage mate for bearded dragons, would be another type of semi-arid Australian lizard. Frilled dragons, though growing larger than dragons, may be compatable in a sufficiently large cage. As Frilled dragons are more arboreal than bearded dragons, a large tall cage may work for both. Something along the lines of 6'x3'x4 (LxWxH) for a single bearded dragon and a single frilled lizard. You would need to create both low and high basking areas and multiple feeding areas (frilled dragons, if I recall correctly, eat insects and occasional small mouse pinkies) as well as good sources of UVB lights (mercury vapor bulbs may work best in a setup like this).
All in all, for the amount of extra work, larger cage, constant observation to ensure neither animal is stressed by other cage mates, it will be much simpler to house different species of lizards in single cages, instead of putting them into one large cage.
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PHLdyPayne