I've used herptivite for years with veiled chameleons and none of them ever showed vitamin A issues. I would think if a chameleon species eats some vegetation it would be likely that it could convert beta carotene.
What do you feed/gutload the insects with?
As for the study you talked about...not sure I believe it.
I’ve been gutloading crickets and roaches with Mazuri Iguana Diet, a vegetable based meal. Also with fresh mustard greens, carrots, oranges, squash and whatever vegetables I save before cooking dinner.
Ingredients:
Dehulled soybean meal, dehydrated alfalfa meal, ground soybean hulls, wheat middlings, ground corn, dicalcium phosphate, calcium carbonate, soybean oil, salt, DL-methionine, cholecalciferol (vitamin D3), pyridoxine hydrochloride, l-ascorbyl-2-polyphosphate (vitamin C), menadione dimethylpyrimidinol bisulfite (vitamin K), d-alpha tocopheryl acetate (natural source vitamin E), folic acid, vitamin A acetate, calcium pantothenate, biotin, thiamin mononitrate, ethoxyquin (a preservative), choline chloride, vitamin B12 supplement, riboflavin, nicotinic acid, manganous oxide, zinc oxide, ferrous carbonate, copper sulfate, zinc sulfate, calcium iodate, cobalt carbonate, sodium selenite.