It probably would depend on the brand of wiffle ball and how hard it is. The gap between the wheel and the stop plate is about 1/4 inch less than the diameter of a ball, so that ball gets squeezed before it is shot out the other side.
Add to that the fact that most wiffle balls have holes in them that restrict their flight, and you'd certainly never get a pitching machine to throw a wiffle ball 60 feet to a batter. You'd have to move the machine much closer to get the ball to cross the plate.
This machine can throw the Heater lite balls and soft lite balls; though, I'd stick with them!