From what I understand, it was Charles Frazier's first book and he won the National Book Award with it and got the movie deal. Not bad, IMHO.
I do share the same opinion with you about using bluegrass musicians and others outside of the old-time realm for the music, but I was real glad to see Riley and Dirk involved.
The musical references in the book are inaccurate, too.
Specifically, what musical references in the book are inaccurate?