No, Elvis didn't steal. He took songs (blues, gospel, country songs..) and made them completely different, completely his own. His "Milk Cow Blues Boogie" sounds nothing at all like the original. His "Hound Dog" is a rock song, the original is a deep blues song.
Elvis, I guess you don't know, was a rock artist. He took blues, country western, gospel tunes, anything he loved, and with Scotty and Bill, made them rock. It was absolutely brilliant what he did in the early years. Heard a song and interpreted it his way --- in other words, rock.
Elvis didn't steal. He completely changed songs. The Rolling Stones were playing blues songs as blues songs. That's stealing.