I have heard some of the rumors too but never put much credence in them. Maybe because back in my teens and twenties, I kept hearing rumors of Satanic influences in just about EVRY rock song. Every song I checked backwards sounded like gibberish and I eventually assumed I was being conned by the same people trying to convince me that dancing, cards, pool, and alcohol were all Satanic. Maybe I was wrong about Zepp. I need to revisit that issue as far as they are concerned. I still get a good vibe from listening to Robert Plant however. He seems to have turned out all right.
My early Christian years were all extremely legalistic Southern Baptist not quite to the stage of snake handling (but probably within sight of the snake box). I am still a very Committed Protestant but I have learned to check everything I am told without automatically relying on everything I am told by people claiming to be devout. The scourge of the Pharisees is still alive and well in the church (Not at all calling you one, you bring up a good point worthy of investigation)