Yes, we used credits at the snack area behind the Fantasmic seating when we went in January on the Quick Service Dining Plan.
We were able to use snack credits for popcorn, frozen lemonade, Mickey ice cream bars, and a few other things I don't remember.
It wasn't a problem at all and was much more convenient to find a seat and send DH to go get snacks instead of trucking them all the way up the path to the show area.
Have fun!