I agree with the PP, except I would like to add extremely not probable.
We do breakfast at 'Ohana's every trip and the amount of people waiting for a table is ridiculous. We always have ADR's but still end up waiting around 15 to 20 minutes.
I stayed at The Poly in November and I did eat at O'Hana's for breakfast and Dinner..the wait with a reservation is 10-15 minutes and there was ALWAYS tons of people waiting..If you were staying at the Poly you can try but I wouldn't plan a trip to The Poly for a walk-up. Call the Disney dining line even when you are on your trip..most people who cancel do it the day before or the day of..good luck!
I got lucky a few times doing that!
Thanks everyone. I had a feeling it wasn't likely. This was a last minute, let's go there before hitting the road to drive home idea. I'll try calling and see if we can get an ADR between now and then.