Thinking back to our stay at the Dusun, I remember two steps from the garden floor into the outdoor kitchen. Once you've managed those it is wheelchair accessible I would say (no more stairs/steps) but you best check with the hotel management directly.
But it is true, getting around with a wheelchair in Bali should better be done by use of a driver and an appropriate vehicle, and even then getting from the car into shops and restaurants will be a challenge most of the times, I assume. But Balinese people are very helpful. That said, Bali is a great place to visit and even though it's easy to say for someone who does not need a wheelchair, maybe a wheelchair should not stop you from going there, if you plan accordingly.
Yes ... the one I stayed in was.
Certainly the one we had wasnt as it had a couple of steps at the gate and another at the main villa entrance. Sorry I dont know about the others.
I agree, Bali in general is not good for wheelchairs - you would need to rely on drivers/taxis, they are cheap though :)
Get an answer from The Dusun staff and past guests.