I would just keep an eye on him. I also have a green spotter puffer in my tank for around 8 months now. I got him when he was maybe 3/4 inch and he is over 2 inches now. He hasn't eaten any inverts, and I got plenty of snails, hermits, and starfish. I have never seen him pick on the corals either. ( i have lps and softies) I feed him normally with all the other fish, such as blood worms, mysis, brine, ect. Also a note I added more snails, hermit, and a red star fish AFTER he was in and no problems. Then again I just may be lucky. I think he should be ok though, from my experience.
Tj