Is it legal to land when an airfield is reporting low IFR due to fog with a visual approach? Suppose you are on an IFR flight plan and are coming in to land at your destination.  

The weather at the destination is reporting 600RVR due to dense fog.  The fog isn't very high as you can see through the fog while on approach and can see the approach lights and part of the runway lights.  The weather above the fog layer is VMC. The lowest visibility for an ILS approach that can be executed by the pilots is 1800RVR.   


Can the pilots accept a visual approach even though the airport is reporting IMC?
Are there other factors that should be considered on an approach like this?
A visual approach can not be authorized by ATC during true IMC.


  5–4–23 Visual Approach
  a. A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the airport. The pilot must have either the airport or the preceding identified aircraft in sight. This approach must be authorized and controlled by the appropriate air traffic control facility. Reported weather at the airport must have a ceiling at or above 1,000 feet and visibility 3 miles or greater. ATC may authorize this type approach when it will be operationally beneficial. Visual approaches are an IFR procedure conducted under IFR in visual meteorological conditions. Cloud clearance requirements of 14 CFR Section 91.155 are not applicable, unless required by operation specifications.