As the title mentioned. And also, is using it in zero visibility (or near) a real life scenario?
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.
No, the use of a VOR is not considered flying IFR. Although you can fly IFR using a VOR for navigation. You can also fly VFR using a VOR for navigation. Radio equipment other than VOR can also be used for navigation in both IFR and VFR flight. And, flying IFR in zero visibility is a real life scenario. But, you can not use a VOR by itself to land in zero visibility.
You can fly both IFR and VFR without using a VOR or even having one installed/operational in the aircraft (depending on aircraft certification). Though, if a VOR is used for navigation, it must have been inspected as functional and accurate by a certificated pilot within the preceding 30 days of the flight for which it is being used.
IFR (Instrument Flying Rules) is a set of rules, procedures, and regulations governing the flight of aircraft solely with reference to flight instruments instead of the ground. You can fly IFR in IMC (Instrument Meteorological Conditions) or in VMC (Visual Meteorological Conditions).
IMC would preclude referencing the horizon. But, it would not necessarily mean that you have zero visibility. You can not fly VFR in IMC unless you remain in sufficient visual conditions to maintain specific distances from clouds and specific visibility.
These rules include requirements for specific equipment for the aircraft and training for the pilot. Navigation equipment is included on the list of equipment. Although a VOR can be used to satisfy the navigation equipment requirements, a VOR is not specifically required. GPS is a suitable radio receiver which can be used for both IFR and VFR operations instead of or in addition to VOR. In some areas of the world, an NBD/ADF receiver would suffice. In the past other systems like LORAN would have been included in the list of suitable radio navigation equipment.
Think of it this way. Flying IFR means to fly by flight instruments only. A VOR receiver and indicator are not flight instruments. They are navigation instruments. The only navigation instrument that is specifically required by regulations for IFR flight is a DME (or DME equivalent like a GPS) above Flight Level 240. Otherwise navigation equipment is included in the requirement for radios pertinent to route of flight. Radios pertinent to flight is already required in the stipulation to maintain two-way radio communication with ATC.
Title 14 of the Code of Federal Regulations Part 91.205
(d) Instrument flight rules. For IFR flight, the following instruments and equipment are required:
(1) Instruments and equipment specified in paragraph (b) of this section, and, for night flight, instruments and equipment specified in paragraph (c) of this section.
(2) Two-way radio communication and navigation equipment suitable for the route to be flown.
(3) Gyroscopic rate-of-turn indicator, except on the following aircraft:
(i) Airplanes with a third attitude instrument system usable through flight attitudes of 360 degrees of pitch and roll and installed in accordance with the instrument requirements prescribed in §121.305(j) of this chapter; and
(ii) Rotorcraft with a third attitude instrument system usable through flight attitudes of ±80 degrees of pitch and ±120 degrees of roll and installed in accordance with §29.1303(g) of this chapter.
(4) Slip-skid indicator.
(5) Sensitive altimeter adjustable for barometric pressure.
(6) A clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation.
(7) Generator or alternator of adequate capacity.
(8) Gyroscopic pitch and bank indicator (artificial horizon).
(9) Gyroscopic direction indicator (directional gyro or equivalent).
(e) Flight at and above 24,000 feet MSL (FL 240). If VOR navigation equipment is required under paragraph (d)(2) of this section, no person may operate a U.S.-registered civil aircraft within the 50 states and the District of Columbia at or above FL 240 unless that aircraft is equipped with approved DME or a suitable RNAV system. When the DME or RNAV system required by this paragraph fails at and above FL 240, the pilot in command of the aircraft must notify ATC immediately, and then may continue operations at and above FL 240 to the next airport of intended landing where repairs or replacement of the equipment can be made.
VORs are central instruments for both VFR and IFR flying. A VOR is used in VFR flight often to facilitate long distance navigation or find relative position with respect to various VORs/Airports around the aircraft.
For example, an aircraft with a dual VOR system can tune one to Station A, one to Station B, and then take the bearings/headings of the two to interpolate and determine an approximate location (by intersection of the bearings). VORs can be used to plan cross country flights as well, but GPS is becoming more user friendly and accurate.
For IFR flight, VORs are often very important as well. Especially in a non-glass (ie G1000) aircraft, VORs are used to describe IFR Low En-Route Airways - the Victor Airways crisscrossing the United States. They are not considered "required" for IFR flight, but most IFR routes can be flown using Victor airways and hence VORs. VOR approaches are now more deprecated but plenty exist - I just did one a few days ago! A VOR approach is like a localizer approach - non precision, with higher minimums. There are technically "no" IFR approaches that allow for "zero-visibility" - every approach in IFR conditions has a minimum as denoted on the approach plate (IAP).
Here is an IAP for a VOR approach: https://resources.globalair.com/dtpp/globalair_00998V27L.PDF
Note the "S-27L" minimum of 520ft MSL and 1 SM visibility (520-1). A VOR approach has higher minimums than the average RNAV, LNAV, or even Localizer approach because it is not considered accurate enough to take an aircraft to 200-400 feet above the ground. An ILS, which is a precision approach, usually has a minimum of 200-300ft.
So in general, there are no approaches allowed at "zero visibility." Some airliners can do a "Cat III ILS" down to much lower minimums than even a standard ILS, but definitely not with a VOR.
I hope this helps! :)