As far as I know, nobody has released anything using the oscillators directly, but I've played with it a bit, mainly trying out phasing effects. (it was a bit boring, with perfect digital oscillators)
The potential is there for music notes, but there's a lot of data to feed to setup the oscillators, and with 1 byte a frame, you need to account for the delay in note timing. (you could setup the oscillator in advance, and just give it volume as a "note on" a few frames early) Also makes it a bit tough for chords, though maybe some frames of delay between notes might make it more like guitar strumming.
In 21 Blue, I used tuning on voice phonemes to make it sing along with the short intro tune. I think that method is a fair bit easier to manage, and is a bit more striking.