Vitamin D3 promotes the absorption of calcium into the bones, as well as helps to regulate the calcium: phosphate balance in the body.
Thus, an amount of vit. D3 is essential to chameleons in the prevention of MBD.
Vitamin D3 is naturally produced in the reptile's body when it is exposed to UVB radiation. The best source of this radiation is from natural sunlight, however UVB lights made specially for keeping reptiles also allow the animals to produce vit. D3 in their skin, and this is the primary reason reptiles are kept under UVB lights.
Vit. D3 can also be administered to chameleons in the form of supplements such as the calcium with D3 that you are referring to. However, supplemented vit. D3 can build up in the reptile's system and actually hinder the calcium absorption process.
So to keep things in balance, vit. D3 is supplemented sparingly. Usually pure calcium (no D3) is dusted with at the majority of dustings, with D3 being used less frequently. The general rule is that if your cham is exposed to natural sunlight, than D3 supplementation should occur less frequently, but if the cham never gets access to sunlight, then slighty more frequent D3 dustings are needed (for instance, babies can get D3 dustings once a week, but adults only twice a month, and adults who are getting regular sunshine down to dustings with D3 only once a month).
Some keepers prefer not to use any supplemented D3 at all, and rather try to increase their chams' exposure to natural, unfiltered sunlight.
Note that:
"in studies of iguanas [Bernard et al.], those iguanas receiving Vitamin D3 injections or diet supplements fared less well than those iguanas whose main source of D3 was from ultraviolet radiation." (
Calcium metabolism and MBD)
So the summary answer is: yes, you can use calcium with vit. D3, but you should use it sparingly and certainly not at every dusting. Instead, you should be using pure calcium (phosphorus and vitamin free) at most feedings.