I've never read anything about VitA in particular, but it is a fat-soluable vitamin just like D3. So I would imagine you'd need to be careful with how much they are getting. But unless you were dusting your feeders with VitA, I highly doubt they'll get enough of it to do any harm.
but is your reptile eating the fluker's light fixtures or gauges? i don't think so. i was gutloading crickets with fluker's cricket feed and it gave my leo serious diarrhea. not a happy gecko. but as soon as i gave him mealworms fed with bedding from cricketfood.com, boy could you see the difference. he's much more active and healthy, and i know it's much better for him.