My opinion has always been that published versus self-published is a way to describe a book, not an author. there is nothing at all to stop authors from pursuing both options. Unless of course your publisher invests in your career so thoroughly and successfully that it is only fair to work exclusively with them in return.
Rebel Ink, on the other hand, thinks that "We prefer to work with authors
that are interested in developing a professional relationship in lieu of
self-publishing. While self-publishing can be a worthwhile and
enriching endeavor, it is our experience that authors do best with both
feet firmly planted in one world or the other, not both."
For any author preparing to have that conversation with them I would recommend asking: so, what's in it for me? Other than the same thing that every other small e-publisher is providing, that is. Me, personally? I think authors working in the small press arena are wise to diversify.