Belfast,

People get royalties for arrangements of traditional songs. I receive royalties for my folk arrangements from Mel Bay, my publisher.

I am not aware of litigation concerning violation of "arrangements of a folk song". In most cases there's probably not enough money at stake to warrant taking the claim to court. Even if you filed a suit for artistic reasons, you'd still have to pay lawyers, prove the case, win it in court , and (the hard part) collect damages. The damages in most cases being small.

There are many cases involving authorship of songs, and rewrites of songs.

-Richie