You'd have to be pretty crazy to ally with LA Ermor, in my opinion. The disadvantages on the long term severely outweigh any short term advantages. Unless, I guess, someone is steam-rolling you and you're really desperate for an ally.
It's tough for one nation to take on Ermor alone, and in a no diplo game, there can't be any formations of alliances and coordination of attacks, which I think is very much to Ermor's favor.
But I don't mind, I'm Marignon after all. Bring all the undead you can.