You can write portlets using whatever technology you see fit. How you write your portlets is outside of the Portal scope. As long as the portlets are JSR-168 or JSR-286 compliant, they should work.
The question however is: does web framework X provide a bridge between the web app and portlet worlds? We happen to think that JSF / Seam / RichFaces are good matches for portlet development and we provide a bridge for these technologies that integrate well with Portal. Other web frameworks might work as well but, once again, it is really outside of the Portal scope and more up to each web framework to provide a bridge to the portlet world.
Ok, considering that it is still Age of Innocence w.r.t JBoss Portal for me, I had a question.
Suppose, there is an application in web framework X and X does not have the "bridge"; then how will it be surfaced in JBoss Portal ?
Rewriting already a stable app in Seam/RichFaces must not be a binding option. I am sure the development effort to rewrite apps and ease of integrating running apps(in various frameworks) into JBoss Portal must have been looked into ?
The simple answer is: it won't. Portal works with portlets. Any web application cannot be deployed within it and expected to work. I work on the Portal itself, not on portlets so I don't have much experience on whether X framework would work well in a portal context or not, unfortunately. Basically, without a bridge, chances to get your app to work in Portal (or any portal for that matter) are close to none without some work. How much work is required depends on the web framework you are using. Sometimes, the only option is web scrapping.
Which web framework are you using?