BLUE TONGUE SKINKS

Hey, just a quick one, I generally stick to chicken or turkey grain free dog food with few ingredients to make sure ventress isn't having anything that he shouldn't have, but I've started wondering if he can have different ones such as duck, lamb etc and how closely do we need to check the ingredients Veg wise? I see some have things such as chicory root etc and stuff that isn't on the diet sheet, so is there anything specific in some dog foods to avoid? Just want to give him as much variety as possible, he does also have Veg, bugs from time to time etc.
Thanks