I think it depends on your idea of "idol worship" In Christianity one of the 10 Commandments is:
"You shall have no other gods before me” (Ex 20:3).c.
“You shall not make for yourself any carved image” (Ex 20:4).
So if you actually worship Elvis as your God in life and death-then I think you are running into trouble with the Christian faith.
I think Elvis loved to be loved-but he was always careful to warn fans that the one true King was in Heaven.
Also in his singing of religious music he was in essence pointing to that King in Heaven and saying "How Great Thou Art" each time.
Bumper stickers are fun, but having one on a vehicle is a far cry from serious discussion of religion.
Elvis was a sinner, but so is every single person since the Garden of Eden. IMO Sin is sin- from the biggest ones such as murder, to the smallest white lie. We all have to atone to God and walk our path in a personal way. So I see little conflict in Elvis's life that I can not identify with (but naturally not in the exact circumstance just in the idea that we all sin)