They don’t need to know if you are on the dining plan in order to make a ADR. They don’t have a set # of tables for dining plan guests. You can wait until you check in for your ADR to tell them you are on the dining plan. The only exception might be the ones that require a deposit (princess bfasts and fantasmic dinner pkg. etc). Although, when you book those you are still required to give credit card even if you tell them you’re on the dining plan. They don’t really need to know you’re on the dining plan until the check comes but it’s a good idea to go ahead and let them know. That way your server can help you make choices that fit the plan.