Most light splash lenses are plastic. I would just try to let it dissolve with water. Vinegar works on coralline because vinegar is an acid and coralline is a base( carbonate). I'm not sure if it will work on salt creep.
Just so you know too, salt creep on lights conducts electricity. So if the creep is on the lights, down to the tank, it can put voltage into the water. If you can, figure out a way to make a shield, so the splash doesn't make it to the lights. Creep on them too, will destroy them pretty quick, inside and out.....I speak from experience!!