FODPLod, remember that RN Pilots/Observers can be asked to carry out watches on the Bridge at sea as THE OOW or 2nd OOW whenever they are embarked. They don't just do it when they are too senior to fly on ops. RN Pilots/ Observers are Seaman Officers first & aviators second (whether they like it or not!)
Indeed they are often REQUIRED to carry out Bridge watchkeeping duties to keep themselves current iaw the requirements of maritime law & the watchkeeping certification requirements. If nothing else this helps them maintain their whole ship knowledge & contributes to a whole ship "aviation-maritime mindset".
I have no doubt that the RAF Merlin force could transfer to the CHF, perhaps with a few RN/RM aircrew bodies to help their assimilation to the role but they would have to immerse themselves the CHF role fully, become ship aware & safe (members of fire fighting and damage control parties, even get involved with storing ship & replensishing at sea etc - Yes, Officers do that too) and when embarked they may be expected to help out in the Ops Room, FlyCo or on the Bridge when not flying. Effectively they would become the FAA & undisputedly orphoned from the RAF. Do you want that? Fine if you do, welcome.