I know this was covered in the Gord series, but refresh my memory here? Who were these guys? More importantly, how have they been used in canon.... for example FtA in the Sea Princes revolt?
they were??? I recall no mention of a black brotherhood in the Gord Books (although admitadly I read them long ago, and not very closey as I found the writing horrible)... the only mentions of the Black Brotherhood that I recall off the top of my head are in I1 Dweller's of the Forbidden City, where they are mentioned in a section about designing your own adventures in the area, with no real details given, and a few years back when Erik Mona was talking about the black brotherhood as a splinter sect of the scarlet brotherhood that had taken to worshiping Tharzy (something about this might have been in SKR's scarlet brotherhood accessory, but I don't remember for sure).
Anyway, the BB is a splinter group of the SB that discovered "something" while investigating ruins in the Sea of Dust and - apparently - converted to the worship of Tharizdun. They tried to use the resources of the SB to bring about the return of their mad deity but were discovered by other members of the SB, leading to a sort of covert civil war since then.
The first mention of their existence is, indeed, in the old I1 module.
We can infer that since the SB fellas in Artifact of Evil actually were trying to get the Theopart and use it to release big T, that they were BB.
The revolt in the Hold broke out when loyal members of the SB discovered that the Herdsmen in the Hold were heavily infiltrated by BB, who were sniffing around big T ruins in the mountains.
My take on it was that the leadership of the SB in the Hold were the real BB fellas - hence their ability to direct operations towards sniffing out big T ruins. Some of their non-BB subordinates, however, discovered this and tried to arrest and overthrow them. The leaders declared the subordinates traitors and accused them of being BB to muddy the waters. The subordinates were (mostly) all killed, leaving the remaining SB enclaves in the Hold in the hands of big T worshipping BB agents.
An article on Canonfire listed a yuan'ti city in the Hool and said that they had an alliance with SB and that some purebloods were used as spies.
I developed a yuan'ti double agent, a cleric of Tharizdun, working for the Black Brotherhood, seeking to use a theorpart of the Artifact of Evil, plus the Cult of the Blackflame, to further their ends. I've even managed to pull in the Return to the Temple of Elemental Evil now as well!
It's a bit convoluted since my own character (who is in charge of the Keep of Adlerweg from the Sentinel) is a shadow mage (now converted to a shadowcaster) who became one after playing Baltron's beacon where her soul became tainted by the blackflame as a plot device for the class conversion.
There is loads of potential in that region for espionage and counter-espionage, plus it looks as if the Gauntlet might have resurfaced in some of the teasers... watch out Denha...