Unfortunately, at least what I heard when talking with vets in the past, is they don't really learn much of anything about chinchillas in vet school, it's a single page in the text book in the chapter on "pocket pets" (which covers rodents, reptiles, and small birds and fish). If they want to learn more about chinchillas they need to specialize in rodents, where there are more in depth courses they can take, or do their own research. There really isn't much draw for vets to specialize in rodents like there is for cats, dogs, and even exotic vets tend to specialize in birds or reptiles, there are sadly a lot of people that simply don't take rodents to the vet at all so not much money to be made there. Knowing more then the vet was one thing that really bugged me when I would take my chins to the vet when I was a kid, I felt like why am I paying for an exotic vet when I know more then they do?
Unfortunately there really isn't much in terms of actual scientific research or articles out there, even about diet, most of it is simply observations of people that own chinchillas. They give their chins fresh greens and their chin ends up with gas and/or diarrhea. I really think one reason the vets don't clue in on that is people don't mention it or even take their chins to the vet for that. Maybe if people start mentioning that when they tried giving some it upset their chin's stomach vets might start realizing it's a problem. The people that would have the number of chins and the money would be ranchers, and since they just feed hay, pellets, and water (no greens or even treats) and never had any issues with malnutrition (which would effect the fur quality) they aren't going to motivated to spend the money on researching other things to add to the diet. Kind of a "if it's not broken don't fix it" situation. If chins can live long lives, some well into their teens and even 20s (especially when in the wild they only like 5-10 years), on just a simple diet I take that as proof that they don't need additional things added.
I don't really take what the vet says to heart even for my cats and dogs though, most also didn't study nutrition, so likely are going off what they heard or read. I do my own research and figure out why this or that ingredient is or isn't good for them and make my own decision on what to feed.