Diplomacy is tricky at best Pretty much a case by case scenario and most of the time not always apparent as to why. Some of the alliances or hostilities that has occured is based on a lie. For example GMG's hatred of Kruger is based on the popular belief (both sides of the border) that Kruger started The Eighty Year War. When even secret to most of Rheinland is the fact that it was Daumann that manipulated the war into starting.
Obvious diplomacy is certainly found everywhere, however, and can give the appearance of black and white. There's even seemingly complicated diplomacy that isn't so complicated after all (I've come to learn long ago that "the enemy of my enemy is my friend" is an utter lie).
Oh, yeah GMG hires Reavers and knows Hogs have hired Reavers for their own things as well. They are just hired guns, if they were hired specifically to come at GMG we'd just engage those mercs with more money, something GMG has no shortage of XD.