The controller is perfectly compatible as far as I can tell. The turbo feature on the 3rd partly Genesis controllers is really nice, too.
The only thing that bugs me is that the build quality of the controllers is pretty bad, so they tend to go bad quite often. The conroller I got was the one built into the Genesis 3 remake, and the right button doesn't work at all. I bought two more controllers, and the ABC buttons are flakey on both. Hmph.
So, how do you get Dreamcast controllers working on an Amiga? :-D