The project was created 2 years ago by seam-gen, and the code assist did work last time I needed it. In the meantime I had to switch from Eclipse Ganymede to Galileo, because JbossTools VPE was causing Ganymede shut down when opening xhtml file (https://jira.jboss.org/jira/browse/JBIDE-3993)
As for the richfaces-ui-3.3.0.GA.jar, I do not have it in .classpath, but I never had as I see in svn. Adding it changes nothing though, the assist box is still not there for most tags..