No experience, but the questions your asking are viable and make sense.

I would think that it would be a good idea to supplement his diet to keep him as healthy as possible. I don't think that aptasia carry much nutritional value. But on the other end of the sword you don't want him to get a taste for finer foods and start to ignore the aptasia for tastier foods. Then again its part of its prey instinct to go after the little PITAs, you can't ever take that away from someone or something.

I would be more worried about the 6 sea rats you put into your tank munching on corals rather than the aptasia.