To be honest they were straight up satanic and its well documented. Especially Page. He bought alistair crowleys home so he could become even closer to the one he worshipped. I grew up in the 80s as a kid when everyone from Ozzie to ACDC was accused of being satanic. None of them actually were...as far as i know theres no proof regarding any of them. Led Zeppelin is a whole different ball of wax. Sucks because Bonham was great and they made some good music. I am not listening to satanic stuff though regardless of how great the musicians making it might be. No thanks.
Some cool factoids here based on what I recall reading over the years:
Page was certainly fascinated by the occult back in the day. No denying that.
Ozzy (maybe my favorite) has never been satanic. The only one that tried to get into that in the Black Sabbath band was Geezer Butler, the Black Sabbath bassist. One night, he claims a black specter appeared before him. He felt that it was basically asking if he was really in, or out. Scared the heck out of him, and he turned away from it. When he told his band mates about it, Ozzy, Bill Ward, and Tony Iomi were terrified. They all (Including Butler) started wearing big crosses for a while afterwards to try to ward off the evil. Sabbath just wanted to sound spooky with their music....and they did.
ACDC's name came from a tag on one of their sisters vacuum cleaners. Alternating current, direct current. That's it. The song Highway to Hell it a nickname for a highway in Australia near where one of them grew up. Hell Bells was written because they didn't think Bon Scott made it to the pearly gates. They were never satanic at all. They are just a bluesy, hard rock band.
I watched a recent interview with the lead vocalist from Slayer. He seemed like a cool guy with a good sense of humor. He was asked why they put on the scary, evil persona. He stated that back in the mid 80's when they were trying to break in L.A., that all the bands started putting on make-up to make themselves look like girls. They didn't want to do any of that crap. They decided they just would to scare people. He said they put on the persona just to, in his words, "F*** with people". Seems they aren't satanists at all.