I think all of the following are in the public domain, meaning that while various artists may have copyrighted arrangements, the tunes themselves are traditional and do not require clearance to include their performance in a film (assuming the performer is cleared):

Whoa, Mule, Whoa

Salt Creek

Cripple Creek

Pig In A Pen

My check of the BMI website would seem to confirm my assumption: for each of these, the credited "writers" cover several generations and genres, meaning that the copyrights are almost certainly for arrangements, not for the tune itself.

Does anyone have any knowledge of any of the above having been written by a known individual? Thanks for all input.