This thread looks like a topical point to mention something that I just had happen to me, though I know this is probably old-hat to the veterans of the game...
In a fort I was building this weekend my first year's (Summer 301) Human caravan came with its assorted human Merchants, protected by Hammerdwarfs, Speardwarfs and Axedwarfs (which isn't something I'd paid attention to, before, but I assume is fairly usual). But alongside them was "Zolak Utesespo, Goblin Outpost Liaison", the Diplomat.
Had to do a double-take, on that one when I saw the entry on the Unit List, but trade (and diplomatic discussions) went ahead as expected, and the Goblin civilisation is still listed under the Petty Annoyance/Death import/export style of diplomacy, so it
was on behalf of the humans after all.
Anyhoo, apropos of the subject of this thread: if kidnapped dwarfkids can come back in later assaults as enemies, and the humans manage to employ diverse humanoids in official capacities beyond merely those of mercenaries, then why not something (perhaps an application of Stockholm Syndrome?) that can be applied not only to beasts passively caged, but also to captured beings?
(Actually, the number of times I've accidentally let a mountain goat escape and cause havoc in my Dwarven Halls, meaning I've had to send one or other branch of the military in there to slice it up because it was averse to the adhoc cage traps I tried to set up... I really need to perfect some way of non-lethally herding these occasionally troublesome creatures (occasionaly precious but as yet untrained breeding stock) that's akin to the "capture, not kill" idea...)