A Big Bill Broonzy session from the late 1930s included a bassist identified as something like "probably Wilbur Ware" or "Wilbur Ware (?)" - even though Wilbur would have been only 14 or 15 at the time, he was precocious, so we shouldn't be surprised.
Surely a lot of jazz musicians still play on R&B stage shows.
Ike Rodgers isn't thought of as a jazz musician, but his soulful trombone playing on some records by obscure blues singers of 80+ years ago is what (for me) makes those records valuable.
Completely off the subject: Charles Brown once told me he was raised to play classical piano, didn't play blues at all until adulthood.