DS restaurants do take ADR through the Disney system. I’d try to get one if possible. Last minute is a good time to check as tables normally open up as people finalize last minute plans.
However, if you don’t see anything through Disney, don’t give up. You have a much better chance of eating at a DS restaurant without an ADR then you do at restaurants in the parks. Many of the restaurants in DS only release a portion of their tables to Disney. The rest they leave available for the general public. You can usually get a seat by calling the restaurant directly to make a reservation, booking through Open Table, or even making a walk up reservation same day.
You should be fine 3 days out.