Sounds like a viable idea for a hack.
I'll have a look at the myspace mp3 player, which probably uses flashvars to call the mp3's. It would require the memberinfo template to be modified to enable the player to show within a persons profile, whether this can be done using vbulletin's hook system I wouldn't know, since hook locations have changed in the past few updates. The postbit, does offer an hook, which would mean we could easily add details using the product XML system.
I only looked at this thread because I designed a flash-based profile and that uses its own mp3 player. It looks a bit out-dated now since I haven't had the time to update it. You can check it out at
www.myspace.com/syrusxl
I'll look into this and give some feedback.