Do I need to drill a hole into new granite counter tops for an exsisting dishwasher overflow valve?

Wait a minute. What you're talking about is an "air gap" that breaks any pressure lock preventing the dishwasher from draining. You don't need an air gap if you have a disposer (food grinder) under your sink. Food grinders have a fitting with a knockout that will take an adapter available at any hardware store. The adapter will connect the drain hose from your dishwasher to the food grinder, eliminating the need for another air gap, and also eliminating the need for another hole in your countertop.