To the point of the thread--Blind Blake style guitar rags, jug band music, and Travis-picking, and the like have always been an integral part of the the American folk scene, and that stuff is all jazz--

Also, the legendary folk scenes, at least in SF and NYC tended to cohabitate with the jazz scenes, though those were progressive jazz scenes, not traditional--it certainly wasn't uncommon to see John Coltrane LP's next to Mississippi John Hurt on those cinderblock record shelves that we all had--