In Moodle, which roles appear as participants and which don't?

Please answer this question if you can, and then change the tag.

In Moodle 1.7 it seems that admins don’t show up as participants in individual Moodle sites. Are there any other roles that hide that way? Is it something we can turn on for a given role?

One use case we’re trying to solve is that we need to give dept. webtechs permissions to view, edit and update and assign roles to their class sites, but we don’t want all their names showing up in the Participants list and confusing the instructor.