I'm a bit confused now too. How are a few posts of interaction between players (and given you "just added them to encourage activity", there is interest?!) a barrier of entry. Sorry, but if a couple of posts between RM and UC players to register your UC character on a BB are too much for you, I really don't know what kind of activity this should spark.
And yes, UC ventures to Cologne. Though that doesn't really imply anywhere that they're known in Rheinland for services UC offers within Gallia for Gallia.
The Hudson infocards clearly state that BHG's base is there for a goddamn reason. Because BOTH Liberty and Rheinland considered it the correct move. Keep it to Rheinland + BHG as pre-registered, let the rest RP it out okay.