Hello Nick! The noise channel was often reserved just for Pokemon moves/actions/battle-cries to minimize how much they would have to interrupt the music when sound effects played. You do not have to omit drums if you end up making a red/blue style theme though (even if you make a traditional Gameboy chiptune track with only 4 channels)! FireRed and LeafGreen could be good references to look at if you'd like an idea of what drums could look like structurally in the original tracks (if you haven't checked them out already)