In general we consider Sakai data to be controlled by the owners of a site. The fact that data is stored in Sakai doesn't give staff any right to access files or other information, except in very specific situations:
Other than routine support and investigations of system problems, the other types of access should be authorized by the Director or Associate Director.
Note that a Dean, Director or Dept Chair doesn't automatically have the right to access information of their faculty or students, unless there is a specific policy permitting it, or an official investigation as outlined above.
If there is reason to worry that data may be deleted or changed, staff may make a copy of data for safe keeping, but not give it to anyone except as described above.
While we don't have a practical way to limit what the owners of a site can do with data submitted to a site, there are limits imposed by law and University policy. The basic policy is the University copyright policy.
Most material in Sakai will be owned and potentially copyright by the person that created it, although the copyright policy defines exceptions. Putting it in Sakai does not change ownership. However the copyright policy says that "The university, however, retains the right to use student works for pedagogical, scholarly, and administrative purposes." That permits student work submitted to Sakai sites to be used for ordinary teaching, such as grading, feedback and discussions, by members of the site. There would be similar implicit permission for work put in a site by faculty, staff and guests. This does not mean that members of a site may take work in the site created by others, and republish it or otherwise use it outside the site, except where there are policies or agreements that would permit it.