I understand the Grand Hotel Excelsior Vittoria has an elevator to take you down to the marina. Does anyone know if the public can use the elevator or is it controlled by having a room key card?
This may be of help
The elevator is public so can be used by anyone - for the fees noted - during the hours it is in operation. It's the same lift that was discussed in your post about Marina Piccola 73.
We used an elevator in the park near Imperial Hotel Tramontano. This park near Villa Communale has a lift in the left corner of the garden that is open to the public for 1 Euro single trip and 1.9 Euros return. This park also has a lovely view of the bay and Mt Vesuvius. The lift brings you down to the beach area and Marina Piccola.
I believe the first two posts are conflating two different elevators. The giant luxury hotels built right on the cliffside, some of which have the word Grand in their name, mostly have fixed wooden swimming decks down at the Gulf level. These are reached by private elevators that go to the hotel lobbies, for hotel guests only.
These elevators are not useful for going to ferries at the marinas because the swimming platforms are quite private, and connected to nothing else.
There is, indeed, a public elevator to the tiny, diesel-scented beach and marina area, which costs a Euro or two. It has posted hours and has occasionally been reported to be closed. It often has a line to get in. But I've ridden it without problems, after being tendered in from a cruise ship, for example.