Thinking of the future value of knowing skaven we might face, it's worth looking at the local map of the Underempire.
There are four major routes leading into the City of Pillars from the Underempire, and there are four tunnels that lead to no known surface features within a couple of hundred miles, which I've marked with green stars. Presumably these once lead to minor dwarf holds, which I'd expect to now be minor skaven warrens. We're also only just over two hundred miles from the major skaven warren underneath what was Karak Azgal, which isn't far if you take the warprailway train. One of those green stars may be Karak Azul, but as Kazador exterminated the local skaven, it's not marked as a major warren...
As a side note, based on the scale, it's about one hundred and seventy five miles from Karak Drazh to Karak Eight Peaks via the Underway, and the orcs don't have trains or super-radios like the skaven do. That means it should take quite a while for orcs to traverse it. I don't know how we can exploit that, but that communications and logistics gap must be something we can work with at some point.
The map contours are also interesting. You can see that Death Pass isn't that far above the level of the Badland all the way to the Dark Lands.