Lonesome EJ-
The tune to "Silkie" that you refer to is by no means traditional (or it least it waasn't when James Waters wrote it). I believe that the copyeight was assigned to someone named Sandy Paton.

It's still not clear whether Johnny I Hardly Knew You came before or after When Johnny Comes Marching Home, but the real popularization of the tune was when they shifted the rhythm a bit and came up with "Ghost Riders In The Sky"