Of course they know. Every church member and every independent non church Scientologist knows about Hubbard's early writing career and his background (though his background in occultism is sanitized/barely hinted at). So what? I don't give a crap who created what. I'm interested in ideas.
I am a Scientologist and a former Church of Scientology member and this doesn't bother me at all. And let me tell you something, I'm a former Christian, too, and I've done a LOT of reading about various other religions. They all were made up by science fiction writers from where I sit. Only thing I found in Scn was that the techniques and theories are based on what a person experiences and feels for himself. I wasn't told to have faith in some deity I could not see.