well feed them off as they first emerge and sorta white in colour and soft. I wouldn't give too many "mature" beetles as a regular feeder they are quite hard... But a few here and there won't hurt. hope this helps.
Yes, you can offer the beetles to your chameleon. IMHO mealworms should form no more than 10% of your chameleons diet, and the same goes for the adult beetles. I would not offer these (or anything else for that matter) daily.
A varied diet is best. Aim to have no one feeder make up more than 20% of your chameleons diet if possible. Certainly any feeder that you provide more often than that ought to be of the best possible types, and well gutloaded.