I don't see why they don't support it.
According to J.W. D3 feels even better with a controller.
"With some of our early experiments in putting a direct control scheme into the game via a 360-like analogue controller, I've been 'Oh this feels even better, with direct control…'"
I thought as much, you get much better precision moving a thumb stick. Clicking feels very unnatural with some of the escape abilities.