I believe that you are doing it wrong when simplifying the relations between the factions in Kusari. This House offers the great opportunities of character and faction roleplay especially because everything is complex and the contradicting ideologies and conspiracy are all over the place. Canon roleplay is canon roleplay and the Black Dragon Society is following it for Hogosha. This group utilized Mercenary ID as a generic one especially to play a non-canon game, based on the actual interests of the sides of conflict. Hadn't I mentioned that it's a totally alternative way for Hogosha in the disclaimer?
We can start the discussion of the canon in another thread if you want, it would be interesting given that most of the factions tend to ignore the most interesting parts of its lore.
Kusari had no problems with the Hogosha pirating the living hell out of every trader passing by regardless of affiliation and destination (with the rule-wise exceptions, of course), yet you assume that the Hogosha-affilated group which follows the Hogosha interests in continuing their timeserving makes no sense. Yomotsuhisame hadn't been caught with their dirty business yet, though, once it happens even the Black Dragon Society would proclaim them the traitors of the Empire. And all that time the Yomotsuhisame would serve Hogosha's best interests.