I think it could work with an entire ocean, although I’m not sure what the best approach would be. Man, thinking about how difficult an ocean shader would be in the first place makes my head spin. Your shader uses translucency, which is why SSR is not an option, right?
I think the two hardest obstacles using the scene capture actors would be resolution and orientation. You’ve probably seen why the scene capture actors make terrible flat mirrors, I think you might run across the same problem with a large body of water, but it depends on the player location. If you are up close to the water an it is reasonably choppy water, you might t get away with it. Although, you would have no way of capturing local reflections. Stuff like ships on water. The capture would really only render the sky and very large assets in the distance. The more I think about it, the more difficult I think it might be.
You could try parenting the scene capture to your player pawn. Then the reflections would be more localized, but you might run into a whole host of other problems. Hopefully Epic will eventually add SSR to translucent materials, or a scene capture reflect actor, like in the old days of UDK. It is entirely possible that all the necessary tools already exist, but we are just unaware of how to uncover them. Usually the case in my experience. lol