Its not a good idea to house the two of them together for several reasons...it will likely stress them out....chameleons are generally solitary animals. In the wild they have enough space to move away from one another if they want to...in captivity in small cages, its impossible.
The Senegal is likely WC and comes from a different area than the veileds do so they could each carry different bacteria, parasites, etc. A chameleon might be able to deal with "its own" bacteria but that from another area might be too much for it.
If they are left together they may try to mate...and IMHO its not a good idea to cross-breed the species. (It might be different if they would naturally cross in the wild.)