I've had a similar question a while back but using C++ on OSX. I've ended up using the ofxHardwareDriver class which is a neat little wrapper for a few libfreenect functionalities(accelerometer, LED, Motor) and can run side by side with OpenNI.
The catch is you can use the libfreenect driver and the openni driver at the same time only on Linux(as sudo)/OSX but not on Windows. If you simply need the depth map and motor access, libfreenect should suffice and there is a C# wrapper for libfreenect.
If you need skeleton tracking and motor control on Windows perhaps you should try the official Microsoft Kinect SDK which is C# friendly.
Update: There might be another half-way option: mskinect-openni-bridge but I haven't tried it myself.