unfortunately it is not possible as JSF technology is not really good at being an aggregation technology for portlets.
can't i use some JSF / RichFaces components in my tabs.jsp, for instance to draw the pages navigation tab?
say i place tabs.jsp in my own WAR and configure the portal to use it from there. would it them be possible?
no it is not possible, unless you create a theme that does not use a JSP but rather uses a portlet defined as a special region.