Here was the situation. I was in a dwarf faction. We had two goals: control the underground section of the map (7/12 locations) and take back a Karak (held by orcs). A skaven faction also had to control the underground, and an orc faction had to hold the Karak. We dwarfs realized that we couldn't fight both at the same time.
So I came up with a plan, working with one of the Skaven players. The Skaven would allow us to have 5/12 underground sections, and we'd let them have 7/12. It would give the dwarfs a fluffy supply line, and most of the "dwarf sections" of the underground. In return, the Skaven would turn their attentions to betraying their NPC Skaven allies, and we dwarfs would focus on killing orcs.
I tried selling it to our NPC leader by saying that it wasn't that we were friends with the Skaven, we were just allowing one Skaven clan to betray another while we focus on killing orcs. Our NPC figurehead threatened to take the Slayer oath if we even talked to the Skaven. So...in the end the Skaven kicked the living crud out of us, and we had to retreat out of the underground completely. The campaign just ended with the Karak's underground entrance completely collapsed, and the tunnels leading to it flooded (to keep the Skaven out, as they were gearing up to join the Karak fight after they beat us in the underground).
So the question is this: from a pure background point of view, could you see dwarfs doing this? IE: Agreeing not to attack Skaven so that they can focus on other enemies? Or, as many of our players argued, when faced with overwhelming odds should we have just did what we did: grit our teeth and make a few heroic lasts stands?