Just perused
http://www.alpina-automobiles.com
The Alpina B7 xDrive does have Dynamic Drive ( Active Roll Stabilisation ). Thus xDrive and DD are certainly compatible.
I conclude that BMW excised DD from being bundled with 750i xDrive MY 2011, for financial reasons. They simply felt that customers should pay extra for it!
Alpina have made the decision to bundle xDrive and Dynamic Drive because their research shows that both systems implemented concurrently, promote optimal driving.
This has reinforced my decision to make sure that my 750i xDrive ( non-Alpina ) comes with Dynamic Drive.
The beauty of DD is that active anti-roll stabilisers on the front & rear axles minimise car body roll eg when cornering or in sudden changes in direction.
The result is a better performing car. Perhaps I'm a little too intense but I crave for a vivid encounter between man, machine and motorway anytime I step into the car. If it is affordable I'm willing to spend to achieve that level of experience.