Elvis had a massive, massive influence on R&R and blues singers/musicians.
Some of the people who don't like him are usually those who were around and "active" when he was and they were into something else.
Its a bit like Nile Rodgers, who I don't happen to like [or do I?], having a big influence on R&B and other types of music since the 70's.
Wasn't particularly into that disco stuff at the time, though I do appreciate it has it's place in the grand scheme of things.