Heck no. You don't need to "officially" be a playwright to create theatre or work with us. If you are a director, an actor/performer, or anyone (even a playwright) who wishes to develop a piece in a way which is somewhat different from writing and revising drafts of a script we want to hear from you.
Personally I have directed a few such projects: a cabaret style solo performance piece which played at the Minnesota Fringe Festival, a solo piece adapted from Molly Bloom's stream of consciousness section of Ulysses for Bloomsday, and group created performance pieces. Playwrights aren't the only folks who create theatre and we want to serve everyone interested in creating new works for the theatre.
Take a look at our submissions page and send us your idea (you may also want to look at the playwrights page to get an idea of what I mean by workshop). We're capable of supporting a variety of models of development of new work. If you have any questions, please email us at info@ptwks.org.