For the UK sector, the CAA took control of the limits for sea state after the various puma issues prompted them to act, the limit is dependant on the aircraft limit or demonstrated capability, in practice this is significant wave height of 6m as indicated on the offshore met office weather website.
The offshore weather reports (regardless of sea state) indicate that recovery is or is not available for a flight, this only applies to the immediate area around a rig since landing and takeoff are deemed to be the most critical phases. So would only ask if rescue is available if they had ommitted this required piece of info from their standard weather report.
Some ask, some don't, some weather reports specify it without being asked, some don't, it is an approved method, though many think it shouldn't be. Rescue vessels are not obliged to offer rescue in sea states that aircraft can legally fly over. When the operators manuals said fly up to 7m in accordance with the OGP guidelines, it was often the standby boat that went u/s before the sea state for flying, not so much now 6m is the limit.
Some do, some don't.