CAPT FLIES APCH WITH WX RPTED BELOW MINIMUMS IN SPITE OF FO'S OBJECTIONS.

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ATIS ON DSCNT TO OMA RPTED 100 FT SCATTERED 1/2 MI VISIBILITY AND MIST. UPON CHK-IN INTO OMA APCH; THE RPTED RVR WAS 1400 FT FOR RWY 14R. I ADVISED THE CTLR WE NEEDED 1800 FT RVR TO SHOOT THE APCH. AFTER DSCNT CLRNC TO 3000 FT; THE CTLR RPTED 2600 FT RVR FOR RWY 14R. UPON CONTINUED VECTORING FOR RWY 14R; THE APCH CTLR RPTED 1400 FT RVR (INDIRECTLY ASKING US OF OUR INTENTIONS). WE HAD THE COMPLETE RWY 14R RWY AND CTRLINE LIGHTS IN SIGHT FROM ABOUT 10 MI OUT. THE CAPT STATED THIS TO ME; AND TOLD ME TO RPT THE FIELD IN SIGHT AND ASK FOR A VISUAL APCH. KNOWING A VISUAL APCH IS NOT AVAILABLE WHEN THE ARPT IN IMC; I ADVISED THE APCH CTLR THAT WE HAD RWY 14R IN SIGHT. THE CTLR CLRED US TO INTERCEPT THE RWY 14R LOC AND MAINTAIN 3000 FT; WHICH THE CAPT DID. I ADVISED THE CAPT THAT WE WERE NOT LEGAL TO COMMENCE THIS APCH. THE CTLR STATED 1400 FT RVR RWY 14R (INTENTIONS?). THE CAPT TOLD ME TO RPT RWY 14R AND ASK FOR A VISUAL APCH. I TOLD THE CTLR WE HAD RWY 14R IN SIGHT. AT ABOUT 2-3 MI OUTSIDE THE FAF; THE CTLR CLRED US FOR THE ILS RWY 14R AND CONTACT THE TWR. UPON CONTACTING THE TWR AT THE FAF; THE TWR RPTED RVR RWY 14R AT 1400 FT; AND CLRED US TO LAND. I STATED TO THE CAPT; AT LEAST 3 TIMES THROUGHOUT THE APCH; THAT WE WERE NOT LEGAL TO SHOOT THIS APCH (USING CERTAIN EXPLETIVES TO EMPHASIZE MY OBJECTIONS). THE CAPT STATED WE WERE LNDG! WE HAD FUEL FOR OUR ALTERNATE PLUS ABOUT 1 HR 15 MINS RESERVE. THE CAPT WAS DETERMINED TO LAND; AT ABOUT 1000 FT AGL. I CONCEDED TO MYSELF THAT AT THIS POINT THE SAFEST THING TO DO WAS TO COMPLETE MY BEFORE LNDG DUTIES. ALONG FOR THE RIDE WE LANDED SAFELY; BUT CLRLY ILLEGAL ON RWY 14R.