First of all, I don't think, that Simon Petrovich is Cowl. Why? "Where is the Russian?" Cowl, from what I can remember, has a Germanic accent. Not Russian.
Langtry is a politician. He does what he can to stay in power and keep the White council together. That's why people who rebel aren't liked by him.
Camp Kaboom was hit some time before White Night.
Cowl doesn't like "the bad man Kemmler". Maybe we've seen his character, maybe not. It might be interesting, but I don't recall any characters with a German [ ok, it's also possible to be Netherland ] accent. But given, that Die Lieder des Erlkönigs were collected in Germany, he is already familiar with summoning Herne the Hunter.