Does the VISOR afford Geordi this capability?
Yes. In TNG : The Masterpiece Society we learn that his VISOR...
...scans the electromagnetic spectrum between one hertz and one hundred thousand terahertz, converts it all to usable frequencies and carries the information directly to the brain.
As such, Geordie's vision ranges from the deep radio band, through infra-red and well into the ultra-violet. That would easily allow him to see in the dark, even if the visible band was totally absent.