Gammons is a pretty good guitar player. He performs a couple times a year at a club in Boston to raise money for charity. Theo Epstein also plays guitar and has a band... and is part of that local-rock-for-charity thing.
Bronson Arroyo actually released a CD when he was here, he's also pretty good. He did a cover of The Standells' "Dirty Water" with some of the 04 Sox players singing backup (including Johnny Damon).