Interesting, but a bit misleading. I was expecting something more like HotJava, where the entire thing is java top to bottom. A webkit wrapper for Selenium tests is definitely useful, just not as neat as the idea of a pure java browser.
It uses only Java SE. It implements the Selenium API and wraps the renderer and JS engine that's built in to Java (WebKit). Granted, Java itself is built on native code and native WebKit renderer (whereas, the networking code, graphics, cookie management, headers, etc. are Java). Sorry to be misleading.