A bonsai is not a type of tree, it is a way of pruning and altering a tree to keep it short while still growing a thick trunk. Any type of tree or shrub can be made into a bonsai. I have a ficus bonsai that is 15 years old. So it just depends on what kind of tree they used. Make sense?
as shauna said, assuming you get a safe plant in bonsai form you will be fine
HOWEVER, take note that bonsai's do have some special care requirements. I have no experience with them, but I would be wary of anything that may conflict with the chameleon (off the top of my head, I would think that the bonsai would drown from too much water?)
not saying its not doable but there may be more to it than a typical plant....the bonsai experts can hopefully clear that up
They make bonsai Ficus benjamina trees, but I wouldn't recommend putting something that requires so much effort and time into a chameleon cage to get pooped on.