It will work, the question is how long. Small metal parts such as screws, springs and axles will corrode more quickly. When used in salt water aquariums: Immersion depth must be at least 35 cm (dry-running switch)

I don't know whether it works in seawater. But I use it in a pool with an electrolytic cell, and the water is also salted there.
salted. It works perfectly there.

In theory it should work but for logic I would advise you every time to rinse the hoover in fresh water after use otherwise the salt stays in, hardens and could damage the product. I would get a bucket of fresh water and start it inside so that it gets clean inside. I hope I've been helpful. Anyway it works great and we practically always have clean water without turning on the filter.