mmm, it's a bit debatable.
Chris has mentioned a bit here and there of his occult dabblings in various interviews, but there's nothing he's said that's really placed him in a single stone.
There is a bit of significance to certain songs of theirs however. For example, the reason that they couldn't print the lyrics for The Siren of the Woods with Theli is because their record label wouldn't allow them to print the translation for it.
He is a member of some massively diverse scholarly group of occult studies, but I can't remember the name of it. It's somewhere on wiki and google if you spend some time digging up some dirt.
Either way, he just uses it musically for concepts. Nothing to take as what would be considered ritualistic, or of targeting the audience. If it is ritualistic at all, I'd imagine that it'd be deeply personal for him, and probably unknown to be so publically.
Tell ya what, if I meet him, I'll ask him myself.