The answer to this question is Yes and No.
The ability of the photosites(a.k.a Pixels) to see a larger range of lights from white to black(a.k.a Dynamic Range) depends very much on the sizes of these photosites hence the larger the photosites the more light it can take in hence better sensitivity so call. As FX sensor is abt >2x bigger than the DX sensor similarly the FX's pixel sizes is also bigger than that of the DX's. So comparing the D700 12mp whose pixel size is, say >2x than that of the D7k's pixel hence, Yes, the D700 does have better DR over than that of the D7k.
However you may argue that D7k has 16mp hence higher resolution than the D700 but there is so much more to pixel density that Diffraction may set in at a mid f5.6 or thereabout as compared to a 16mp FX cam, which the pixel sizes is still bigger than a 16mp DX cam. Unless the replacement D700x/s (whatever they may call it) has a 36 or 48mp FX body and the pixel size of the FX now becomes smaller than the DX, then the DX will hv a better DR than FX.