Well, I think it does quite a bit more than just reading/writing MIDI files. From the description:
> Play with OSS drivers, play with spkr(4), Play on Windows, Export as .wav (very slow and very low-fi).
So it might at least have example code for accessing the MIDI interface in Linux (OSS) and Windows.
I agree, though, that the easiest method for most use cases is just to pre-synthesize, but if download size is a consideration, MIDI (MOD, IT, XM, etc.) playing would be nice. Then again, maybe some kind of installer that converts the MIDI, etc. files to OGG on the user's computer would be feasible...