Recently read an interview with the late great Muddy Waters. He said that while there are many fine white blues instrumentalists (exact quote was "some of them can play rings around you") none of them can "vocalize like the black man". He had a point IMHO.
OTOH the late great jazz saxophonist Lester Young said his favorite blues vocal performance of all time was Frank Sinatra's take on "Blues In The Night". Of course Sinatra didn't try to sound like a black man when he sang the blues.