You have to be an officer to be a pilot in any of the forces but you can apparently fly a helicopter in the army without having to be an officer but enough about that because this is a RM forum.
And yes aircrewman is available as a specialisation in the marines.
Taken from main RM website... Aircrewman
As an Aircrewman, you will fly on board the helicopters of the Commando Naval Air Squadrons. Trained to operate by day or night, and in all conditions, you will carry out important missions from reconnaissance to helping transport troops or supplies to the front line.