AFAIK Oculus doesn't use stereoscopic 3D so it's frame rate is irrelevant as far as the 3D is concern. (too an extend)
However, if nVidia can integrate G-Sync in 3D Vision, then the GPU can control the framerate so it's better than having VSync on.
The FPS is not so much important in stereoscopic 3D, the only thing is that the effective frame rate is halve, so if it's 30 then each eye sees 15 and can start to distinguish individual frame. nVidia wants 120Hz because PC master race.