How do you add sound to a region?

I'm looking to have a song play whenever the player's camera pans into the region covering my graveyard and fade out when the player's camera pans out of the region.

So far I haven't seen anything that plays music in a region, but I did find the action "Add/Remove 3D sound across region." Would that work? I'm still confused about the 3D part, since my file is just an imported mp3 would that still work?

The only way is to try. Make sure your file is available via the sound manager, then try it out with the trigger.

If it works, then yes. Otherwise, no.

add the sound you want as a "3D" sound in the sound editor,
double klick the region you want and chosse the sound you want for it at "environment sound"

the sound is a bit quiet then but it works