The Accorded nations would have to respect such an organization if only because it could tell the military where to shoot. They could raise layered ward around important sites. Not strong enough to stop an incursion, but enough to slow the initial rush and summon security that would normally be stopped by hexed equipment. Just putting up circles around crucial areas is priceless.
I like this idea but it could quickly become unwieldy and I could see it fracturing into regional and national squabbles.
I suppose it depends on the nature of the Librarians.
I like the idea of them being the current iteration of a timeless organization that has existed for nearly five thousand years, moving from continent to continent, collecting knowledge and artifacts but not getting involved because they understand the natural order of things, as well as that they are largely powerless in the face of such beings.
But they could also be an obnoxious, corrupt bureaucracy with over-confident, self-inflated mortals that think themselves superior because they know a bit about things others don't.
Given that Butcher has hinted at mortal resources being brought to bear against the supernatural, I'm inclined to think they'll be more like the former than the latter.
But so far we've every mortal authority (SI, CPD IA, FBI) all be asshats. If the agents seen in Dog Men are from the Librarians, then I'm not optimistic. If they're more like Agent Tilly, then maybe it'll work out