Interestingly, I've noticed that the Serpentis have way more agents in Curse (55) than in Fountain (13), despite the fact that the latter serves as their headquarters and whatnot. They also took over ORE Syndicate, of course, which only has 17 agents total, all in Outer Ring (naturally).
You could take this in several different ways, ranging from assuming it doesn't reflect anything in particular IC to thinking that the Cartel does have a large influence over the Serpentis and wants to keep them close.
On a side note, this may change at higher levels, but Angel Cartel agents have not assigned me any L1s against the Republic. Lots of activity against the Federation, some against the Khanid (and of course CONCORD and Sansha), but nothing against the Republic. I'm pondering how to take that IC.