Good luck with this! Sounds like a good integration tool. Shortly before I faded out of Source plugin coding, I wrote a vBulletin plugin that acted as a bridge to SourceBans. Whenever a user was added to the defined "Admin groups" in the forums, SourceBans was updated to reflect that as well. Even worked with vBB's subscriptions.
I have no idea if it still works, since its been over a year and SourceBans may have changed.