I don't know much about the Shootout, but my guess is that, if someone wants Arc there, they need to go and write whatever programs the Shootout requires you to write in order to participate in the Shootout.

I'd try it, but I don't know Arc (or Lisp yet, for that matter). If someone here knows Arc and wants to see it in the Shootout, I suggest they look into the faq: http://shootout.alioth.debian.org/u32q/faq.php