The Beggar Wrote:

That's because there are no deity power entities among them beyond a rare few (Gargauth, Orcus). These entiies gernerally serve the greater deities who inhabit the LE/NE/CE realms and do not have worshipers because they are not known on the material plane.

Know that those who are powerful enough to be known may have a few cultists in a small cave somewhere but are not powerful enough to rank as even a demi-god due to the fact they have no portfolio to speak of.

Does that mean the entire Book of Vile Darkness is not canon?

No, it merely means that in our setting we don't see fit to add in every single minor power that grants some sort of fiendish spell list or power. It would be overly time consuming and not give anything to the game.

Characters are able to worship any power they want, as I stated in the post (in that there -are- minor powers in existance that do get worshipped in FR). You won't get spells from them here, because they are not in, and not relavent to the setting as we desire it/have it set up.

Edit to add: Besides, the BoVD is IMO, merely a book produced for people with no imagination looking to drop cash on another book written to keep the company in business. I don't fault them for keeping themselves in business, but any book out there that is "canon" is usable by the DM at their discretion for that particular campaign. It gives some general idea I suppose at how "evil" evil things really are if you can't figure it out yourself. *shrugs*

The only devils/demons that actively grant spells in the way that gods do are Gargauth, Orcus, and Ithikraszt.

Certainly other worshippers of other devils/demons exist, but to get spells from them as a cleric does would require an app.

And Pazrael/Pazuzu.

Pazuzu isn't recognized internally, only Pazrael.