Yes, they will deliver it to a Disney Resort. I've rented an ECV for numerous trips and I've never had a problem.
I've used Walker in the past, but am trying a new one for this trip. They don't deliver it until I get there so that they can show me how to use it, I already know, but they require it. LOL!!
But yes, Disney is great with ECV rental companies.
We usually rent from Apple Scooters. The ECV is ready and waiting for us at bell services when we arrive at our resort. They pick it up at bell services after we leave for home. We have never had any problem with Apple...very courteous and professional.
I use walkers for last ten years and it is there when I get there is sitting by bell services and they have the key for it. then you have for going to the parks and back to resort for your whole trip.
We are another fan of Walker's Mobility. We've used them every time for my mom's ECV and have never had a problem. It's always waiting for her in bell services and we just drop it off on our last day back to bell services.