AFAIK wiper arms are painted metal. It may be some sort of rubberized paint, but I don't think so. I just seal mine with some Wolfgang Sealant. Klasse AIO would work well though I'm sure.
Mine still look pretty new ... I wipe them with Quikshine, 425, Aquawax, or whatever qd'er I am using while drying. I believe they are a type of aluminum and easy to bend.