So there are two answers to this. One, No. The Widget Framework does not provide a means for doing Interwidget communication. The second, Yes. Pushing content refreshes and information states to other widgets is possible at the UI layer. A simple DWR service and refresh call and easily repaint a widget and it's behavior entirely, and there is also simple jQuery as well.
As much as Widgets appear to be like "portal", they are not. OpenSocial and Jive Apps are definitely more of a parallel to this common Portal request. Hope that helps. =)