Is using a VOR considered IFR or VFR?
You can navigate using VORs under either IFR or VFR. If visibility is zero, hopefully you are flying IFR.
These days, pilots are going to use GPS if at all possible, but if the GPS fails or if the plane doesn’t have GPS, we can fall back to using VORs. Most planes still have one or two VOR receivers for that purpose, even if they’re rarely used.