I have a humu humu in my 150 and started adding some mushrooms and polyps SLOWLY to see what would happen. I now have, mushrooms, polyps, frogspawn, torch, grape coral, ric's, BTA, montipora, green polpys and others. The only thing I have had eaten on was a glove polyp rock, but my tangs were munching on them also. Pulled them out and put them in my 55g. They haven't touched anything, just the glove polyps, I have blue starflake polyps that they haven't bothered either. I started adding these about 6 months or so ago.
Not saying that this is the norm, but this has been my experience with a humu humu with corals.
As for clams I would say no, I buy Roy (the humu humu) fresh clams at the market once in a while and he goes NUTS for them. So does my tangs and porc. puffer.