GB having Z80 is actually a common misconception. In fact it is Sharp's custom CPU that is a 8080 derivative (like Z80) and has a small fraction of Z80 extra features, but that's it. Porting Z80 code to GB CPU is about as complex as porting Z80 code to 8080 - difficult, ineffective, but has been done before.
The worst thing about GB CPU regarding 1-bit music is that is has just as many registers as 8080, i.e. it completely missing Z80's alternative register set and index registers - this will have impact on possible number of channels. Worse than that, it also missing 8080's EX DE,HL opcode that is very useful in beeper engines, and there is a major HW bug with all 16-bit increment/decrement opcodes that leads to sprite display corruption.
Still, it is certainly possible to do something, especially for CGB that has about twice more CPU horsepower, but in general the platform is not very suitable for this kind of things, so it won't perform as well as Z80-powered systems.