Hi Bethany,
You could use groups/groupings to "hide" your dropped students. Just switch them from Group Active to Group Dropped and have all activities available to both groups. Force separate groups in course settings.
Anything done before the groups/groupings are turned on remains visible to all. After that, only to the group.
Oh, oops. I missed "list" in "Participants list." But, actually separate groups works in participants list, too.