I'm not sure if this is really feasible as most of the Nikon DSLR camera's don't like having the mirror up, which is required for video recording, for any length of time. I have used a couple of methods for getting video in from my Nikon D7000 all with varying levels of success.
1. You can use a program called Sofortbild which can 'tether' the Nikon to the mac for live capture.
2. LightRoom has a tether mode which brings in the live image from the camera.
3. Helicon Focus has a tethering section which gives a live image.
4. Use an Eye-Fi card to transfer the video via a wi-fi connection. (Probably too much latency for this to work)
All of these can bring the camera image in to the mac but I doubt if they would be any good even if there was a way of diverting the output into QLab.
There is one other alternative and that is to use the HDMI output (if available on your model) to provide a 1080P feed into a digitiser.
Not sure if this has been of any help.
Cheers,
Chris