Elvis was a huge fan of black performers. Clyde McFatter was one of his favorite singers of all time. Junior Parker and Arthur "Big Boy" Crudup were also major influences. Except for Bill Monroe's "Blue Moon of Kentucky" all of E's early hits were remakes of black songs. While it would be a mistake to say that Memphis in the 50s was desegregated, white kids like Elvis were listening to blues and r&b (not Chuck Berry) and absorbing their influence and songs and performance styles. Even during segregation whites and blacks in the South did have interaction with one another (especially at the pentecostal churches such as E attended as a boy). Sam Phillips started Sun to record black artists and gradually the milieu began to include white artists like Presley. Did Sam turn his back on black artists after E, Johnny Cash, Carl Perkins, and Jerry Lee took off? Unfortunately yes. But it seems to have been as much a business decision as a racial preference (Sam's favorite performer of all time was Howlin' Wolf). Ironically, the civil rights movement made more difficult the type of nascent cross-cultural interchange that was beginning to happen in the mid-50s. Stax ventured into that arena.
The Beatles in a way started out simply replicating the Presley formula. Cover obscure black r&b artists that they loved and tighten up the beat for a white audience.
Ironically Chuck Berry never had much of a black audience. He appealed to restless suburban white teens. If Elvis was the white guy who could sing black, Chuck was the black guy who could sing white and whose music owed as much to the Grand Ole Opry as the Delta Blues. I'd say Elvis was closer geographically and spiritually to the Delta blues than Chuck ever was (even though Chuck was black).
If Elvis stood on any shoulders, they were Clyde McFatter's, Carl Perkin's, Arthur Crudup's, Bill Monroe's, Junior Parker's, Wynonie Harris', etc.--and his versions of their songs were generally superior to the originals.
