All Things Event Hacking

I think what you're looking for is this data?

Dance offsets

Attacks:
Location= 100080 Size= 4 bytes

Wind Song: 100080
Forest Suite: 100084
Desert Aria: 100088
Love Sonata: 10008C
Earth Blues: 100090
Water Rondo: 100094
Dusk Requiem: 100098
Snowman Jazz: 10009C

Backgrounds:
Location= 11FBAB Size= 1 byte

This info is available on http://masterzed.cavesofnarshe.com/ff3.html and just go to "Dance offsets" .

I'm still not sure how the game assigns the background to a specific dance. I've been having the idea for quite some time to custom edit mog's dances and be able to replace the backgrounds as well (like replacing the "Wind Song" background with the background from ultros and typon's battle), but I still have no idea.