While you can back up your music, you normally should not back up your music application's internal database. Best practice for music applications is to store music and internal data separately so this is no problem. In the case of iTunes, you will need to manually exclude its library and other internal data. In Preferences - Backup, add this entry as its own line in the text entry field "exclude files matching wildcard":
This simple exclusion will ensure that SpiderOak ONE backs up your music but doesn't get tripped up with frequently changing application data that in any case doesn't need to be backed up. For more information on what files SpiderOak ONE should and should not back up, see "What data should I back up?".