If you can find it, photograph it, compute an orbit? why not?
'cuz a gas giant bordering an asteroid belt is likely to attract flotsam like an angora sweater attracts cat hair? "Moon" is pretty loosely defined: basically anything that orbits and isn't artificial in origin. Saturn, therefore, only has as few moons as it has because we haven't started counting ring particles. At some point we're gonna have to define the lower bound or the term becomes meaningless.