If memory serves me correctly, I don't think so. The items at those booths tend to be specialty items and cost more than the limited list of inexpensive items you get as snack items on the DDP.
If there is alcohol involved in any of the items, the DDP does not cover alcoholic drinks.
Yes. You can use snack credits at the Food And Wine Fest(well, not sure about this year, but you could last year). We did it last year when we were on the DP. You could only use your credits for items under $4 and, as the PP said, you can't use them for alcoholic drinks(but I'm bettin' you already knew that). Most of our snack credits, in fact, were used at the F&W Fest. booths. I don't recommend wasting your credits on items that are $1 or $2 though. I paid OOP for those. I used the snack credits for most things over about $2.50.
With all the changes in the DP for next year though, I'm highly doubting they'll allow the use of snack credits for next year's festival.
Have a great time....!!
ETA: As the PP stated above about the "limited list" of snack items, the list stopped being limited sometime last year. I know for a few months before we went last year, there was talk of the available snacks being pretty much anything under $4 as long as you couldn't use it for a meal. We found this to be very true and were even able to get a box of Entenmann's donuts for breakfast using ONE snack credit. Bags of chips and candy were part of the list, as well as items at the Main St. Bakery and even the stuff at Goofy's Candy Co. that they dip in choc(or whatever else you want). With that said, I know there are going to be changes to the 2008 DP, and I believe they are going back to that "limited list". I can't be sure if that has gone into effect yet(as far as the snack credits ), but I don't think it has.