Yes, it is evident in the music of the early stones that the music is very much black music updated with electronic instruments and an ensemble. I have a large collection of early 78’s with black musicians from the thirties on, the influence is unmistakable.
Yes, they went back to the roots. Studied all the great blues men. Back to the earliest recordings. They probably even listened to the Alan Lomax stuff, the Georgia Sea Island Singers doing the old slave songs etc.