Easy enough to test. Get a friend (caster hopefully) and have him cast
every buff he has on himself. Keep hitting him with the song and see what
happens.

It seems to me I never get a message when i use the song. No dispel, no
resist, just nothing happens. Is there some trick to the song?

A somewhat of a tangent. My cleric tested his cancel magic (the low lvl
one) on my roomate. Every time I hit him, one random spell effect came off.
I continued to get the success message (Willae looks dispelled or something)
even when he had no buffs.