Sharon Shannon's "Libertango" album begins with a tune called "The Whitestrand Sling" and closes with the same tune overlaid by a (very positive) rap called "What You Make It". You can sample both here.

http://www.legalsounds.com/download-mp3/sharon-shannon/libertango/the-whitestrand-sling/song_1414088

That said, I think that while folk is undoubtedly music, rap qualifies not so much, because it lacks that defining element - a melody.

Cheers,
Michael