There could be a kernel of truth to the story. Alcoholism is endemic in Bethel. Illicit sex happens at Bethel. Every other kind of vice happens at Bethel. Why wouldn't there be incidents of spirit-channelling happening at Bethel? Not that I believe they're actually speaking to any spirits. But look at JW culture - the belief in demons and the belief that dead anointed are in heaven revealing truths to the GB. Isn't it enough to inspire some bethelites to experiment?
I think that's all it is - a few adventurous bethelites experimenting - but this fact is being exaggerated and blown out of proportion and used to accuse the GB of being involved. It's the same with the SI (subliminal images). There were some actual SI in some of the older Watchtower publications like the Live Forever book. This was undoubtedly the work of pranksters in the art dept. But this fact has been blown out of proportion to the point of accusing the GB of being involved in systematically adding SI to the literature. It has gotten to the ridiculous level that many are putting mirror over Watchtower literature to uncover hidden demonic faces - I mean, come on people!