I'm sure there are some who've completely side-stepped traditional publishers in favor of ePublishing, especially those who knew their niche would best be served through an eBook.
As for success, that's a very personal term. If you mean financially successful, publishing at an ePress will not produce the sales (and thus the royalties) as a major publisher, but you can make money publishing eBooks -- especially if your genre is romance which does quite well online. Some Romance ePublishers even offer nice advances and get print versions in brick-and-mortar stores.