This is completely not true. I know about the Beach Boys backwards and forwards and have followed them since I was a very little kid. Take a look at that link and you'll know it's crackpot stuff. It basically says all rock music is from Satan, period.
I agree with candleinthewind's post above that Anton Lavey and all that crap was just kind of a briefly-hip joke to a lot of the in-crowd. I heard SDJ talk about porn and "Deep Throat" in the same light on a talk show shortly before he died- it was just a hip thing for about five minutes.
As to his falling out with Frank, I read one pretty good account ten years ago in a book on the Rat Pack that said that it was all about an interview Sammy gave saying that he was the most talented of the three (Davis, Martin, Sinatra) which is a sense, he certainly was. But Sinatra was enraged- he had done quite a lot for Davis' career, really fought for him, and through the veil of ego he saw the remark as a betrayal.
I can't vouch for that information as definitive, it's just one book I read, but it was a good, well-researched book.