The island has nothing to do with music/sound.
Did you make sure you put the ogg file in the music folder? Do you have a music folder?
Is your description.ext file correct and in the right mission folder?
If you added/changed the desc.ext file while you had your mission called up in the editor, did you reload your mission? Changes to desc.ext do not take effect until you reload the mission.
As you can see, there are all kinds of things that can go wrong with sound files