In the name of science I did an experiment. I gave my half dragon race the egg tags and made a few nest boxes and made some behavior studies.
A fortress civ race WILL use nest boxes if they lay eggs. In fact it seems that a random female will claim a nest box the moment it is built, immediately rush to it, and after a few ticks lay an egg inside it. Of note is that all subjects so far are unmarried. They will then IMMEDIATELY haul the egg to the nearest food stockpile. Noone has eaten the first test egg yet, but it hasn't been very long, and since the race also has [CARNIVORE] it might suffer from the usual carnivore pickyness and wouldn't eat any eggs regardless, so I can't test that definitively.
After a second attempt building two more nests, since my first subject still hangs around her nest but isn't laying, I managed to catch 2 females the moment they laid eggs in the nests and forbid the eggs. Which should allow them to hatch normally.
Since this is a heavily modified custom race there is also a diverse number of castes, and so far, oddly the eggs seem to be of the same or similar caste as the mother. The first test subject was a white dracon, and laid a white egg. The 2nd and third were both black, and laid black eggs.
Another observation is that the owners of the nestsseem to spend all their time there, not working, and only leaving to eat or drink and coming right back.
...more to come as the experimenting continues.
P.S. Further observation shows that the subjects WILL leave the nest to work. Subject 3 is an animal trainer. When I ordered a kennel built she left the nest to build it.