Maybe. I don’t see why Harmony would need to actively choose a metal for it to be allomantically and Feruchemally viable. I think that if another Shard came to Scadrial, interacted with the planet in the same way that created The Metallic Arts, and manifested their Investiture as a physical metal, there would be nothing preventing the metal from being an Allomantic metal. Otherwise, I don’t think Atium would work with allomancy, or Lerasium with hemalurgy.
Edit: Ninja’d.