yes he can see in pitch black, cuz thats how night vision works...its the light already collected in his occular cells that enables him to shift his vision in the ultraviolet spectrum. however, and i think this is the point you're trying to make is proplonged exposure to absolute darness where there is no light after a while his vision will adjust and since there would no longer be an ambient light. not even a little bit, eventually the light built up in his eyes would eventually dissipate, and he wouldnt be able to see in the dark anymore
