No, you can't use a snack credit in a TS restaurant. (It was never a CS restaurant, always a TS, except for the trial CS breakfast they did last year, which was not continued).
The specialty sundaes are way past the cost of a snack credit, if that's what you're thinking of.
There is a take-out area there where you can get ice cream cones, drinks and maybe small sundaes for a snack credit. If all you want is an ice cream cone, don't order dessert inside, and use a snack credit to get a cone at the takeout area.