I imagine that, if it does come into play, it'll be after all the races get a nice do-over on their home turf, meaning Dwarven homelands will have skilled laborers, farms, bedrooms and tasks. It would also seem odd that dwarves are the only ones that you would be able to live off of; humans and elves likely have as many problems as dwarves do with the critters, if to a lesser scale... Dwarves practically build their fortresses on the ratmen's home, while none-mountainous civilizations attract the pesky pests.
(And yes, Warhammer's the game you see in the obscure gaming store with thousands of individual customized miniatures, a rough cardboard city, and guys measuring out things with flexible rulers. It looks dang fun, but good luck finding the cash and time for it.)
That aside, if we want to discuss what ratmen do and what they are, I've always been a big fan of taking dozens of other ideas (This author says this, but this one...), looking to where those ideas originated (Ancient mythology and such), figuring out what would be best for your setting and adding your own ideas and inspiration when possible (So, let's make them like parasitic cavemen). This usually ends up with something unique and original, depending on how much you borrow from others and how much you add or take away.
Pure mythological beings, or their variants, are rarely used (Such as trolls; their females were originally beautiful, magic wielding women, while men were either the same or more along the idea of modern trolls) and they're usually the most entertaining to play with (A Will-o'-Wisp luring adventurers into traps or treasures and such).
So there are plenty of ways to make a unique race of ratmen that are similar to other's interpretations, in that the things are ratmen, but different in many other respects. (If that makes any sense at all. If not, ignore and continue conversation.)
But now I'm just rambling... Hope I got someone thinking, though.
[ August 20, 2007: Message edited by: Dreamer ]