Interestingly, and I hate to feed into any conspiracy theories, but..., there is among occult orders a group of entities often called the Secret Chiefs.
The Secret Chiefs are said to be transcendent cosmic authorities responsible for the operation and moral calibre of the cosmos, or for overseeing the operations of an esoteric organization that manifests outwardly in the form of a magical order or lodge system. Their names and descriptions have varied through time, dependent upon those who reflect their experience of contact with them.
One early and influential source on these august entities is Karl von Eckhartshausen, whose The Cloud Upon The Sanctuary, published in 1795, explained in some detail their character and motivations. Several 19th and 20th centuryoccultists claimed to belong to or to have contacted these Secret Chiefs and made these communications known to others, including H.P. Blavatsky (who called them the "Tibetan Masters"), Dion Fortune (who called them the "esoteric order"), Max Heindel (who called them the "Elder Brothers").
http://en.wikipedia.org/wiki/Secret_Chiefs
But, this is also not explicitly an occult concept and doesn't mean the GB had to have used spiritistic means of contacting entities any more uncommon than prayer, which is also a basic "spiritistic" practice. (Sorry, hard to write that without confusing it with "Spiritualism")
In other words, fundamentally, if you pray, you practice spiritism.