I... don't think that this line of research has been trod, yet. This seems to be something worthy of testing.
First you need to see if they can actually perform labors as livestock/pets. If it is possible, then try making a fort with the dwarves edited so they no longer have strange moods. Then play that fort for a few years with some of the creatures. No strange moods, it's not possible. Is it necessary they should not have [CAN_LEARN]? If not, then try them with it.
However, if you were to make this new creature a new caste as part of the dwarven race, then it may just be possible they can have strange moods. This has an obvious downside of them not being a separate race, of course, and also necessitates them being genderless, as otherwise you'll have servantrace-dwarven marriages, which is really weird... but it may just work, anyways.
The last option is to make them their own entity. Then make their civilization as close to dwarves in values as possible, so they become allies, and inter-mingle, thus allowing them to become citizens in your fort as guests apply for citizenship. Then, make your own little breeding program to marry the creatures so you have a proper class of laborers, similar to breeding animal people for various purposes.
This idea is walking a very thin line between animal abuse and human rights violation.