Well if it involved animals and you worked with a health professional, then strictly under the vmcas directions, no one can crucify you for calling it vet experience. Individual vet schools will move it or keep it under the classification as they see fit, so I wouldn't worry about it too much. I don't think anyone will think less of you for putting it under vet experience. That being said, it might be worth calling up all the vet schools you'll be applying to and take a poll.
I guess in this case, the question is whether this particular PhD counts as a "health professional." I think PhD's are generally considered "health professionals" in the context of biomedical research because whether you have a lab run by a PhD, MD, or DVM, there are many types of research topics/methods that overlap, whereas a PhD's ecology research looking at the relationship between trees and flies... not so much. But then every school is different!