I agree with the others. I think it's okay not to have alcohol served during appetizers. Especially since there will be alcohol later with the meal.
My wedding day is set up in a similar way, and it's not open bar during appetizers...at first I was a bit disappointed and thought it might look like we're being cheap or something...but since we're having a champagne toast right after the ceremony, and then open bar with dinner, I think it will be fine...