not against the rules. I don't know if it's against RP--junkers land on house bases, why cant the houses land on junker bases? Personal opinion is it's lame to use any bases in a foreign house as a launching point for attacks against that house (the locals wouldn't want it for several reasons), but the game seems to depend on this construct at multiple levels (junkers and zoners) so I don't see what can be done about it really.
Maybe congress will FR5 all of BDM and whoever the LN faction is, file a complaint and see what happens