A difficult subject, but most likely not. Unlike today, when game music can be created in almost any way, then used as an MP3 or similar format, it's difficult to realise that, in the 8-bit era, game music was practically a black art, and virtually unrecognised.
Most game musiscians would have their own method of creating music and getting it into a game. In the NES's case, for example, most music is actually part of the game program, since the sound chip is controlled by the CPU. In a sense, creating a tune is identical to coding anything else.
The tune might well have been created on another platform (like a synth or a real instrument) and then ported to use the NES sound and channels, but there's no single way of doing it.
I'd imagine the most common way of doing it would be to set up an interrupt that would frquently call the music program, but it's not my own area of interest. Nonetheless I have a healthy respect for anyone that can produce music on an 8-bit system.
You might be interested to take a look at
http://nesdev.parodius.com/nt2/.
