Last year I decided to find a new vet. My prior clinic was a 2 minute drive and it was inexpensive. They did an ok job but long story short I became dissatisfied with their services.
I took each cat to a different vet. One was maybe 10 minutes away and was non-holistic. I liked what I saw on their website and knew I would get at least some support for my food choices and I liked that they were cat only. Summary: They were better but I wasn't bowled over. The time spent with the vet was maybe 5-10 minutes. Foods for sale included Hills and Eukanuba.
Poppy went to the holistic vet. We spent 45 minutes sitting on the floor in the exam room discussing her. Foods for sale included commercial raw, grainless canned, everything one would like to see for sale in a vet's office. It was a RELIGIOUS experience! I was gushing all the way home, for the entire 30 minute drive and in spite of the whopping bill.
The moral of my story is that holistic vets *seem* to offer better service and do seem to have furthered their education.
But I think you can be an allopathic vet and still offer that same great service and support for alternative and healthy feeding choices. I think you could even adopt some holistic approaches without having to be certified or whatever is required.
I tend to get foggy on exactly what holistic means, and I get it mixed up with homeopathy. So I know my answer isn't quite what you were looking for, but at least it's one customer's opinion. Bottom line is, I'd be just as happy with a non-holistic vet if I got the same great service. Then again, I know that (my) holistic vets are going to take the big-picture view of my cats' health, where a non-hol vet might not....