Being that they seem to be a mix of sentient and semi-sentient tribes, I was thinking that you should be able to incorporate them into your budding kingdom in Fortress mode.
You would have to have a rather high amount of value to your fortress to suitably awe the lesser mortals, and maybe killing a few first would be enough to change their minds about joining you.
Afterward, though, they could be as controllable as your dwarves, minus quite a few skills that wouldn't make sense for them. No planting, no brewing, no masonry, no cooking, etc.
Ensuring that they breed would be entirely up to the player, so if he manages them incorrectly they're just gone for good. In addition, they would have drawbacks: animal-men from the caverns would be unable to go above ground without vomiting, becoming dizzy, being stunned. Animal-men from above ground would lose happiness unless they got enough light.
I like the idea because it would really add some immersion, what with the foreign invader allying with primitive tribes-creatures for use as scouts/muscle against the natural denizens of the caves in return for protection and civilization or some such. The player could reduce his dwarf presence down below, and certain types of animal men would have huge benefits in specific situations such as Amphibian Men clearing out cave crocodiles so your dwarfs can get water or Cave Swallow Men fighting off giant bats to free up your border garrison's attention for that mega-beast coming through.
Some jobs they could have:
Poison-Maker (To create poison from cavern flora that paralyzes, stuns, applicable to not only their darts and spears but to your dwarfs' bolts.)
Herbalist (To gather said cavern flora)
Weaponmaker (Only wooden spears, blowguns, and blowgun darts)
Hunter
Only the actual "animal" men, not the stone/magma/blizzard/iron varieties. Badger and Capybara above ground, Blind Cave Fish, Amphibian, Reptile, Ant, Bat, Cave Swallow men below ground.
I'm sure the idea won't be very popular (it's DWARF fortress, after all) but if it were implemented as just another option in diplomacy it would add more flavor and what I think would be more immersion. To negate any potential benefit, the elves could object to it on the grounds that it's slavery and cruelty to animals all at once.