It's a popular practice to day to sing traditional songs to a lone fiddle accompaniment, but to judge from the comments of later folksong collectors, that practice was extremely rare.

There are one or two interesting examples, though:

Cecil Sharp noted half a dozen songs from Napoleon Fitzgerald, Beechgrove, VA, 24/5/1918, and wrote: "He began by singing in a very loud and untaught voice while he played the fiddle, putting in as many drone notes as he could. At my request he afterwards sang unaccompanied."

The Hensley family, from whom Sharp recorded a number of songs in Carmen, NC, during 1916 , characteristically performed as an ensemble, with Reuben Hensley stating the melody on the fiddle, before his wife and daughter sang the song in unison. Reuben himself sang a couple of snatches of song with the fiddle.

Alan Lomax recorded nine songs from Jim Howard in Hazard, KY, which I rather like.

Those are obviously some time after the Civil War, of course.

On a related matter, I heard the opinion expressed a little while ago that much of what we now think of as Appalachian fiddle repertoire arose from published Scottish collections copied out into tune books for the use of Civil War musicians. I can provide no supporting publications, though. Any comments?