It has been done, in fact I think if you search you can find an old thread where one of the members had done such a thing.
I was just curious, are you planning on doing your Med residency before going to vet school? If that is that case, then you could do some human med (ER shifts, etc) to supplement your vet income.
My main concern would be your loan repayment. Most vet schools will run you $150,000 (less if an in-state school, more for some others) - the avg starting vet salary ranges are from 40-60K (you can find many different estimates) - I don't see how practical paying off $400,000 in student loans (which have sense accrued a TON of interest) would be. Granted, I suppose you could do a vet internship/residency after vet school and if all went well and your earning potential would be slightly higher, but -- I still think loan repayment would be a nightmare.
With that said, if you are really unhappy with human med & KNOW that vet med is what will make you happy - the rest can be worked out... somehow. Maybe seek a financial consultant of some sort sooner rather than later. Although, be sure you know what you are getting in to - the grass isn't always greener on the other side. Try to use your school breaks to shadow vets in different fields and see what you think. (If you haven't already).
EDIT: If I misunderstood your debt amount & you are saying you'll be 200K in debt after both human med & vet med = then I'd say go for it, if you are sure it's what you want to do. However, 200K for both programs seems like a very low estimate, unless you are receiving non-loan assistance (family, savings, med school scholarships, etc)