The refresh rate of your monitor has got nothing to do with your headset. Also, VR games usually run at 90 fps, so the refresh rate of both the Vive and OccRift is 90 hz. I don’t know what kind of flickering you mean exactly but I guess what you saw was either just an aliasing effect or something else that causes artifacts at low resolutions. If what you saw was kind of a ghosting/smearing effect, that’s because reprojection, which kicks in if your computer can’t manage to compute the full 90 frames per second. The game gets locked to 45 fps and the engine is using “older” information to fill in the gaps.
Possibly not 100% correct, since I don’t completely understand it myself 
If you are interested though, here is some valuable information about all of that: