I'm afraid I don't know about the vomiting. One of mine does it occasionally in the morning when I'm about to leave for work---his is linked to the rapid increase in his anxiety over me leaving. He also will throw up if he's injuried, like a cut pad. Somehow he's gotten the idea that throwing up when he feels bad is a way to calm himself down.
I do have another dog, a lab/dobie mix, who had HD. She was diagnosed with it at age six months and had TPO surgery done on both hips shortly after. She got a clean bill of health back in June and since then hasn't slown down at all. It's a blessing and a curse.
Has surgery been mentioned for your's?
Did you have the full thyroid panel done for free T3 and such? I don't know if any of that could cause vomiting, but I have a thyroid disorder myself and when my medicine is out of wack, I get very sick to my stomach. The antibody that marks it is not one that is usually tested and has to specially requested.
Best of luck to you!