You can do veterinary research with either degree. The roles differ somewhat between DVM and PhD, but there’s more overlap than most people would think.
I am a PhD who does research with DVMs. The term “veterinary scientist” isn’t well defined and doesn’t really matter to us. Like I guess I’m a veterinary scientist? There’s a vet on staff in my lab (part-time) and I do work with some large animal models (i.e., bigger than rats) so I could call myself that, but I’ve never thought about it.
People who do research within the vet field come from all sorts of backgrounds and hold all sorts of degrees.
Practically speaking, there’s a lot of overlap in the roles that a DVM and PhD would fill. In our lab, all non-survival surgeries, and some survival surgeries are done by non-DVMs. Our lab DVM does any difficult survival surgeries, and consults on a lot of our other stuff. However, we could do the stuff we do without a DVM if we really needed to. We’d just have to get more help from our institutional vets. Our DVM never did much research before us, so isn’t too helpful with experimental design, data interpretation, etc. However, some other DVMs that have a lot of research experience can and do it all.
Vet school is expensive and hard to get into, while PhD program admission is much easier and you’ll get paid a small stipend while you do it.
However, Job prospects for PhDs in vet science aren’t very good. You’d most likely be looking at working as a poorly-paid technician if you don’t manage to nab the brass ring of getting a job as a principal investigator (a professor running a lab). DVMs can also be lab heads. I’ve known quite a few that don’t practice anymore and just do research. Some DVMs are vet school professors and just teach, others also do research.
DVMs make more money on average, but schooling is crazy expensive and it’s not like most vets are raking it in. So I’d say neither route is guaranteed to be particularly lucrative. Will you be employed? Yes. Will you be well-compensated? Maybe.
The most important thing is to get and stay involved with some sort of biomedical research. You don’t have to work with animals, but it might help you figure out what you’d like to do.