Let's not forget that a lot of those collectors that we revere and to whom we all owe a debt would often ignore their sources when they sang "improbable songs", music hall stuff (the equvalent of pop music). And if the "serious" composers were happy enough to raid the traditional music of the people, surely it's okay for the folkies to take what they want from wherever they like.

BTW the album where tom jones sings with the chieftains is one of the great albums of all time esp the track with the stones.