I think it's possible but undocumented
Look at the Smart Messaging 3.0 document.
It describes the ringtone format - without calling it OTT.
It has values in there for polyphonic and midi ring tones but DOES NOT show the format of data expected for those types - saying it is reserved for the future.
So my guess is Mr.Goodliving (and other Nokia friends) know what the format is even though it is not publicly available.
Come on Nokia support guys - help us make great series 40 games - give us the file format for poly/midi OTTs so that we can play them with Nokia UI on the phones that millions of people currently have.
I am really quite sure it is possible.