The math on this doesn't add up if you were to scale it. If this works, it's only because "vodka made from milk" is a neat marketing ploy that's bringing in premium prices. If several people did this, it would end quickly.
My math:
Milk is about 5% sugar. Typically for distilling you want to get a wash of at least 10% sugar. So for this to add up milk would have to be half the price of 10 brix simple syrup, and it definitely is not. A gallon of 10 brix simple syrup would cost about 40 cents and that's if you're just buying the sugar at a grocery store. Average price of milk is over $3/gallon.
Also, you can buy enough bulk neutral spirits from MGP to fill a bottle of vodka for about 40 cents. It would take 1.6 gallons of milk to end up with that same amount vodka, and that's if your distillery ran at 100%, which it doesn't, so it'd be close to 2 gallons. (I'm comparing retail to retail prices. I don't know