The Vorlons and Shadows, although not a playable race in their own right, are available as supporting characters and fleets, as are Babylon 5, the Drakh and the Interstellar Alliance.
Aside from Alexander, only one other human has been known to have access to Vorlon space: Sebastian, formerly known as Jack the Ripper, whom the Vorlons took from 19th century Earth in order to employ as an "Inquisitor".