Gee, I'm confuesed. If you are flying left seat on the 717 with a FAA certificate, the type rating on the back of it should say DC9. By default that's the same as the 717 or MD80 series. No additional type rating required, but there would be difference training of course. They look the same, but obviously have major systems differences and the cockpit might feel a little strange at first to ya. But a Nine is a Nine is a Nine.
Bill