Ok, I am a little confused. You say you gave them permission to delete users but then say you don't want them to have that permission! Block their access to Delete Users. Just select View Participants instead. That should allow them to see what they need.
This view does not allow them to filter by role. For example, they need to be able to see staff users that have not logged in for a while, or never.
This still remains a very frustrating problem. Any news perhaps?