I think you could say that Scientology is a 21st century holdout of a spiritual movement that had its roots in the 19th century. There's aspects of Theosophy, Golden Dawn, and Crowley-ish stuff that Hubbard tried to incorporate into a "rational" self-help system. It appears he also ripped-off certain aspects of German book published in the '30s called "Scientology: Science of the Constitution and Usefulness of Knowledge" by Dr. Nordenholz.
There were plenty of these sort of quasi-scientific Gnostic movements in and around Southern California mid-Century. Dianetics and Scientology just stuck somehow.
As for the Crowley connection -- Crowley himself isn't strictly "Satanic" (though a Christian might say that we're splitting hairs). Crowley propounded a Gnostic mystery religion that followed a series of revealed truths -- like Freemasonry, and the Rosicrusian groups before it and Scientology after. There were and are plenty of other groups that follow that same template of revealed truths (including early Christianity). In Crowley's belief system, humanity has access to a new evolutionary epoch through the intercession of adepts who use magic and ritual to bring it about. (Sounds like a lot of Indiana Jones gibberish to me)
There were a group of Crowley followers in Pasadena in the thirties, led by a special effects designer and amateur rocket scientist named Jack Parsons. Parsons was also affiliated with a loose circle of science fiction writers, though which he met our pal LRH.
LRH and Parsons did a lot of dabbling in Magick, looking for concrete results, whereas Crowley was peddling vivid metaphors. Crowley heard about their experiments and thought they were idiots who didn't understand Crowley's system at all.
Anyway, LRH ended up ripping off Parsons, stealing his yacht and his wife. Parsons died from a chemical explosion in his garage.
There's a couple of fascinating books about Parsons that feature LRH as a villian : Sex and Rockets: The Occult World of Jack Parsons and Strange Angel: The Otherworldly Life of Rocket Scientist John Whiteside Parsons.