when you say "12 gal" are you referring to a NC12? i know your fish is a juvie, but i honestly don't think you'll be able to keep enuff SPS alive in that small of a setup to sustain the fish (i thought your fish was weaned, BTW). or are you asking for aquascaping reasons? unless you have a chiller, i think you'll REALLY be fighting temp issues if you run MH for the coral.
as far as the fish picking on the coral, one school of thought is that these fish don't actually feed on the coral polyps, but the mucous layer on the coral, with the polyps getting eaten along with the mucous. i read that someplace, but don't recall where. that being said, coral flesh has indeed been found in the stomach contents of dissected specimens.
our pair actively hunts pods in the little stands of hair algae that have popped up and we have left them for that reason. our fish have REALLY taken to pellets in the last month or so.
HTH