Geopolitically, Ulthuan have only recently returned to the Old World and most of the influence they've developed has been in Marienburg, and the relationship between the Empire and Marienburg is already extremely strained, so they don't really have any levers to influence the Empire with. Even if they start rattling sabers there's not really a whole lot they can actually do, short of razing a few fishing villages and failed trading towns on the coasts of Nordland and Ostland that the Norscans already raze every other decade anyway. They don't really have any way to escalate things beyond that short of sailing up the Reik and besieging Altdorf, which would kick off War of the Beard 2 plus Crusades 2 at the same time and Marienburg would probably balk at and refuse to allow in the first place, or sailing up the Schaukel and besieging Tor Lithanel, which is something the Dwarves of the Golden Age couldn't manage.