Are there any differences in the sound hardware on the GB, GBC, & SGB ?

The GB Classic, GB Pocket, SGB, & GBC all use the same sound hardware so programmming is identical for them all.

The SGB, however, has access to some SNES/Super Famicon sound effects as well. SGB games that have specifically been written to use these sound effects can have better sound, as a result, than average GB games.