Now the ghost of the old gent must be mortified to watch what's being done with his fictional works. Despite the fact that they always had more of the science fictional than the supernatural about them there seem to be some people who insist on turning them into theologies. There's a very good overview of this baffling phenomenon in the article "The Influence of H P Lovecraft on Occultism" by K. R. Bolton.
Lovecraft’s horror stories have become not just a literary cult like many others, but a tangible cult of the occult. The Cthulhu Mythos of the Old Gods with Unspeakable names are evoked and worshipped, and respected practitioners of the esoteric use the symbolism and mythos as the basis of a magical system. This essay examines some of the individuals, orders and doctrines of the adherents of the Cthulhu Mythos.
If HPL were alive today to disavow such things would it make any difference? Would it stop any of these magick mummers from lighting candles, putting on robes and consulting ersatz Necronomicons? I doubt it. And just how long it will be before we see the cult of Harry Potter? "That question, so innocent and whimsical then, assumed in my dream a meaning of frenetic and hysterical madness…"