[villagetinker]

If the ladder is stainless steel, NO RUST, if it is Aluminum, NO RUST, is it is steel, I do not care what the coating is I am sure you are going to get rust. So IMHO, find out what the ladder is made of and get aluminum or stainless steel (I would go with SS for a salt water pool). As for an electrical problem, this would not occur just at the water line, as electrolysis would occur over the ENTIRE length in the water, and you would need a good ground connection at the end of the ladder where is contacts the concrete.
A stress crack in the ladder could cause the problem, but this seems doubtful with multiple ladders. Also, there are GFI protectors on all circuits associated with pools, so your can go to your garage and hit the TEST buttons to make sure these are working. If you still have doubts, a good digital volt meter (I have several) connected to a true ground and to a probe in the water will let you know if there is some leakage current.
One other item, if the ladder is a different metal than other metal IN CONTACT WITH THE POOL WATER, you may have effectively created a battery with the salt water as the electrolyte. I am very rusty (no pun intended) on the chemistry involved to cause to corrosion you are seeing.
IMHO, look at all of the pumps, heaters, and any other electrical equipment associated with the pool, and check for proper grounding.
Hope this helps, let us know whet you find, send me a PM if you would like to discuss further.