A lot of offshore ops are Cat B all the time (USA, Brazil and those areas that base their regulatory system along FAA lines)
This is not correct, offshore operations can only be carried out either Cat A or in violation to Cat B since if you do not operate Cat A you can only operate Cat B where H-V is a limitation (for more than 9 passenger seats configurations). But the H-V is only valid for operations over a prepared surface and not over oilrigs where there is no possibility to establish any H-V envelope.