Can't speak specifically for the Glory, but on every ship I've been on, they sit either in the dining room or right outside of the dining room. No, they don't expect a tip for dining choice or table re-assignment.
I saw very few tables for two on the first floor of the Platinmum Dining Room. And, to see the Maitre D during debarkation, they put your name on a list and directed people waitng to see him into a packed lounge near the dining room. Seems everyone onboard with late dinner assignments wanted them changed to early. I guess what I'm trying to say is, they'll try to accomodate everyone, but everyone has to be a little accomodating also. I didn't bother waiting to see him. We enjoyed the late seating and everything else about that cruise.