This is a great list of major players for your social software project, but I would add two other roles: Community Managers and Developers.
SME’s aren’t enough to make a community go, and while the Hubs in the original list come closer, the Community Manager role plays a critical role in community success.
I would argue that developers should make the list. DG clients across the board require legacy system integration of their social platform. As integration is becoming easier in many platforms, the major players still require a developer’s skill set.