What time is Illuminations on the night you have reservations? If the show is at 9, a 6:30 ressie is too early, IMO. Our reservation time in May was 7:25 and I worried it was too early, but we had to wait about 20 minutes past our ressie time before a table was ready. We got a patio seat and it was amazing. Never hurts to ask!
While there is no guarantee of a patio seat, you can ask. If you can't get one and eat inside, there is a private viewing deck for restaurant guests.