I've never seen nor even heard rumors of immersion suits anywhere in the GOM. Helicopter operators do what the customers require. If the oil companies require immersion suits, suspending operations during inclement weather, or anything else, the operators will comply. Since the oil companies apparently don't care, neither do the operators, and short-term cheap is the name of the game, just as it is with the oil companies and pretty much every other company for the past 20+ years. IMO that's one of the primary causes of the present economic crisis.
There are no FAA regulations concerning offshore flights regarding temperature or sea state, so the FAA has no authority to prohibit them without changing the regulations.
The unions are effectively powerless, and have little if any capability to influence operations. Helicopter pilots, at least in the US, simply refuse to stick together for the common good.