yEd supports several export format suitable for web pages (see "File" -> "Export", especially "HTML Flash Viewer", "HTML ImageMap", "SVG", and "PNG"). None of those formats supports user interaction, though (i.e. it is not possible to open closed groups in exported diagrams). However, the "HTML Flash Viewer", "HTML ImageMap", and "SVG" formats support hyper links (see section "URL and Description" in the yEd Manual). Thus, a possible workaround for very few groups would be exporting the diagram twice, once with the group closed and once with the group opened, and link the closed group to the opened version. Of course, if there are several groups in your diagram, this approach is not feasible due to the many different opened versions you would have to create.
