Something to remember about grounding in this particular case, and from a practical viewpoint....the only way a ladder can get 'hot' is if something contacts it from above like a bare wire on an extension cord. If you're working like this you shouldn't be in the water. Even with paint, grease, or anything else, you should still get continuity through the anchors or whatever they're called, that tighten the rails in place. grounding things 'underground' are a different issue because of voltage gradients that can exist in the earth.
Al