In practice, I’ve never once heard of anyone checking for ADRs at a moderate resort though—just the deluxes. YMMV I guess.They generally don’t let people uber to any resort without a dining reservation, including CBR. You could bus or uber to Disney Springs in the morning and take a bus to Riviera. Or take the boat/monorail over to Magic Kingdom from the Polynesian and then take a Riviera bus.
My sister in law tried to get dropped off at Coronado to check it out and they would not let her in if she was not staying there or had a dining reservation. And Coronado is literally attached to nothing.... so, not sure. Could depend on the guard. I would just be ready with an alternate plan if they did not let the uber in- that's all.