I can assure you it is true, they make on secret about it on their website, nor on their sister website which I forget the name of- In fact there was a picture of Heinrich Himmler on that one, who was essentially Hitler's right hand man!
There are plenty of sources out there about Satanism other than LaVey, Michael Ford, Connoly, absolutely thousands of paths which embrace Satanism, which were created before Satanism even became an accepted term!
LaVey popularised Satanism in his atheistic movement, but it existed before and after him in various forms.
But Joy of Satan is full of lunatics, I remember reading once they were all sending negative energy to induce psychic warfare against the archangel Michael....If that is the sort of people you consider to be experts in their field, then the delusion is not exclusive to them.
No understanding of magic, no understanding of Satanism, no understanding of Biblical scripture, no understanding of ancient mythologies, and a strange obsession with UFOs and aliens.