no, frequently harmonies can be beneath the melody line in folk music, although that depends on all sorts of other factors such as whhether it is two part harmony 3 part or 4 part, 2 part harmony can be both above or below the melody line. 3 /4 part can have both as we;ll
listen to this the recruited collier, where the concertina plays harmony both above and below the melody
http://www.youtube.com/watch?v=iEKVeI_VD3E