I *think* they were seating walk-ups in the bar area when we were there a couple of weeks ago but there is very little seating in that space and it was full by 6pm. If you're staying there, there is no harm in asking but I would guess that the are not leaving room for waitlist in the dining room.
It is a hard reservation to get, I think because it's really not that large of a space. I finally snagged one maybe 2 weeks out? We were seated almost immediately, the tables remained full the entire time we were there, and there was no one waiting. So I think they are trying really hard to seat people as soon as they arrive, to avoid a crowd gathering in that small waiting area, which means not likely holding open tables for walk-ins.
Be sure and set up a reservation finder!