Interesting thread. The geneology of Bluegrass is basically...

West African syncopation/Banjo & Banjo Frailing styles meets Anglo-Celtic derived fiddling = Old Time Music

Old Time Music is the precursor to Bluegrass. Bluegrass instrumentally speaking is just Jazzed up Old Time music. You can Bebop-like phrasing (whereas Bob Wills used Swing Jazz in his "WEstern Swing" style) in Bluegrass and should also mention there is a Ragtime element in the Scruggs Banjo style. I remember reading that if you slow down the Scruggs style it sounds along the lines of a Joplin rag.