Why is there no helicopter equivalent to air transport CAT III ILS? This PPrUNe thread discusses that some helicopter manufacturers have tested coupled approaches down to very low visibility minima (perhaps even zero-zero), but it seems that even with the current capability levels of autopilot technology and ILS ground station sophistication, there's no way for a helicopter to land in minima below RVR 1200'/DA 100' (i.e. the "half minima" rule applied to a standard ILS, or a COPTER ILS procedure).
Because many copter autopilots are capable of flying a Cat I ILS to 200AGL, and then descending on autopilot into a hover at a pre-determined altitude above the runway. The pilot can then descend down to the runway surface without any forward visibility. The radar altimeter is used to judge distance to the ground. Because of the unique capabilities of helicopters and their autopilots, Cat II and Cat III are superfluous.
There certainly are few operators who fly to the CAT II ILS minima, one of which is the Cougar Helicopters of Newfoundland, Canada. I know, since I was one of their pilots.
Forward visibility for the CAT II is 600 RVR. The CAT III is not used yet due to the certification issues and few other problems, but I assure you that technology used in the Sikorsky S-92 A is quite capable of this level of service. We most certainly can land on a long runway with worse conditions using the technique described by the RBP, not legally, but in an emergency - when no alternative is left - it could be utilized.
The S-92-B is in the plans now. Its Flight Director will have something called a Rig Approach as a standard feature. It promises to bring the big Helibus to the near 0-0 conditions to any helideck in the middle of an ocean with no runway needed.