What you say, Gordo, is more or less true about Ozark and Appalachian "folk songs" about the war (though descendants of the English were pretty numerous too and producing American folk sings as well). But so many of the songs sung during the Civil War were commercial products written by professionals in Boston and New York, "pop hits" really. The number of folk songs created during the war is very large, but pales in comparison with the output of the pros like George F. Root and Henry C. Work. The South also had a thriving music industry until the economy went belly up.

Just as a footnote, the well-known Yankee song "Marching Through Georgia," by Henry C. Work, didn't come out till March 1865, so it's unlikely that many soldiers got to hear it before the war was over, and probably none in Sherman's army, which was then in North Carolina.

So if you ever see a movie that has CSA soldiers playing "Marching Through Georgia" during the Civil War, it's doubly wrong!