I tried it. Opened an existing album and uploaded a music file. Indeed it was added as a single file/photo. Is it possible to simultaneously play the music while watching the SLIDESHOW (in the Home Menu) or in any photo viewing case, sort of a background music?
Several years ago we thought about letting users pick background music for their entire family site, by uploading an mp3 file or choosing from a library of files. Then the music would play in any page they were on and continue as they navigated through the family site. Or just play it in the front page of the family site. We even thought of bundling some Kleizmer music since that is very touching, heartwarming music. But we never implemented this. It may be time to revisit the notion of background music in family sites. It's a question of taste, and even if the Site Manager loves it, visitors might not love it, but it's about personalization and perhaps we will add this.