I recently ran a big fight in the sewers against skaven. I couldn't help but notice that the ratmen don't have Night Vision. Seems like an oversight. How on earth do Skaven survive and thrive in an underground environment? Lots of lamps? Warpstone nightlights?
Their Observation checks are still decent because of their Scent ability, but everything else was penalized by 2 or more misfortune in the dark. A yellow die on Observation doesn't really make up for 2 black on your attack rolls. Especially for an NPC, since that Observation yellow is at best converted into a black die on the PCs Stealth check.
Just checked the 2nd Ed sourcebook: Old World Bestiary. They had Night Vision in 2nd Ed, but for reasons unknown it was dropped for 3rd Ed.