So I'm more of a backend developer but when I talked to roy about this he said that it could be easily wrapped in a portlet. I'm less sure where SEAM comes into this, but Gavin was working on an example that did registration with SEAM/JBMS. Not sure what SEAM has to do with the JB Collab Client though (aka webmail though after 1.0 that will be inaccurate). Maybe James, Roy and/or Gavin can pipe in about Seam and Portal.
I don't think SEAM fits in this picture at all, but one never knows what the Gavin is cooking.
However, since the ui James Ward created outputs flash, this can easily be deployed in a portal environment, within a portlet.
We have a sample flash portlet running on out live demo: http://portal.demo.jboss.com/. If you go in to editMode, you will see the src of the swf file can be altered.