Of course there is "sea ice", that sometimes forms in salt water seas. The ice crystallization process mostly excludes salt, but the ice contains pockets of concentrated brine, especially if the sea ice is only a few years old. And presumably there could still be salt breezes off the water. (Sea ice, BTW, is different from ice over land, ice shelves and icebergs, because the latter 3 form from precipitation, which is almost completely fresh water. But I haven't skated on them either, because I haven't lived in or visited the right places.)
I've skied on one of the great lakes, and skated and skied on small ponds, but I've never been in a location where I could skate on real sea ice. Have any of you?
If I did, I might rinse the salt off the blade afterwards. I have a 1980's era expensive high carbon steel Techna dive knife that came with instructions that it should be rinsed off after every use.
At one point I tried to look up sacrificial anodes, and wondered whether they make any sense for skating, but I couldn't find anything on it, and gave up. They are common in marine use, and they have been used on cars and trucks - but those are sometimes exposed to salt.
For the most part, on ice skating blades, a combination of using stainless steel blades and taking reasonable care (including, sometimes oil) has eliminated the problem for me. But there are still people on these forums who report problems with rust. So I still find my original question interesting.
And I also wonder whether scratches and rough spots attract rust - and whether that means you should avoid scratching skate blades, but should keep them smooth. Someone said Pennsylvania cars have just as many problems with rust, though they use cinder instead of salt.
I've still somewhere got a bunch of old skates I got when I was thinking about teaching a class on using hand tools to sharpen skates. Maybe I could take a pair, if I can find one that fits, and experiment.