I think it could join you if historically your faction had some kind of relation to the area. The reason Galatia (in Asia Minor) revolts to the Aedui or Arverni (Gauls) is because some Gauls migrated to Asia Minor. Hence the connection.

I believe leaving spies in your towns reduces the chances of enemy spies infiltrating. Since enemy spies decrease public order, less enemy spies=more public order.