I imagine something like it.
In that case you need encriptation extension feature and share the crypt pass key to other people. The idea is administration might have acces anything but that could be crypt, can see document name, but nothing else, content is crypted.
Other thing that can be done in this kind of scenario is some reports to audit to see whos's accessing these special sections ( that can be easilly exploted from activity log stored information and sendind periodically by mail).