True DX lenses will automatically engage 24x 15 mm sensor area by default unless you tell it not to do so. It is in the menue.
The 70/200 is really not FX, but not DX either so it will bring up full frame. You will find the corners weak/soft at 180 +. Stopping down will not repair. You need the new 70/200 VR 11 for best results.
I get great results with my 70-200 VR on my d700. For my uses, it is more for sports and pj work which doesn't need sharp corners. It is a great lens regardless of the format.