They hold the line, at most.
As Penchant said, they haven't participated in any attack, and I don't expect them to. Aurvandil isn't going to be defeated by having more northerners come, it'll be defeated by the Luria-D'Hara war ending.
Well SA's troops they have down south could be quite useful and might end up being a vital part of the war so I am not saying they are not important, just that they have yet to help majorly with the war. And I do not war the Lurian-D'hara war to end quite yet.