Nice little article. The explanation that Dixie came from Jeremiah Dixon's name does seem the more likely of the speculations. Another point is that Emmett called it Dixie's Land. This seems to indicate that someone with the name Dixie (or similar Dixon) was involved with the name.

"Dix" the bank note seems unlikely because it was local paper in the New Orleans area for a rather short time. I doubt that it would have been known in the South generally. Some of the best buildings in the old "French" part of N. O. were built with Spanish capital. Most serious business in N. O. (1810-1850) would have involved French, Spanish, British and American currencies and, of course, notes of credit on banks in major centers and their branches in N. O.

I am keeping my powder dry (sticking with obscure) but someone, somewhere, should have used Dixie in print or in journals or letters before 1859 when Emmett wrote the song. Although most old paper has been lost, I haven't lost hope of someone coming up with the beef.