"Are there any current or former RAN pilots out there? Is it unusual to approach a Ships helo deck downwind?"
The Navy, certainly in my time there, made a very controlled approach to the ship within the SHOL (Ship's Helicopter Operating Limits) being for an approach to land, VERTREP or transfer to any part of the ship designated for such an evolution.
I would have never contemplated making a tactical approach to any part of the ship, even for fast roping practice to the helo deck, let alone an approach downwind.