It is my understanding that MacOSX has a Java API to the Cocoa Framework. The UI would be native Aqua/Cocoa. Sun would probably like to be able to re-use the non MacOS specific parts of the port for thier own purposes.
Of course, they could 'just' port the UI layer of StarOffice to Aqua via the Carbon libs and stick with C++. Then they could go about re-arranging the UI to better conform to the Aqua UI guidelines.