According to the "Bluegrass Songbook" by Peter Wernick, "The Legend of the Rebel Soldier" is by Charlie Moore Copyright Zap Publishing Co., B.M.I, and is based on the Irish classic "Kevin Barry". It has been recorded by both The Country Gentlemen and by Charlie Moore.

I recognize the tune as "Kevin Barry" -- is that the same tune as "Shall My Soul Pass"?

I too doubt that the words to Rebel Soldier go back to the Civil War, they are good enough that they would have appeared in many an anthology of Civil War songs !