Getting the user to log out could be the major problem.

I back up my system everyday and most often Outlook is open.  The .pst file
gets backed up just fine.  I haven't tried a restore.  I would recommend
trying it yourself.  Start Outlook.  Perform an incremental on your system.
 Ensure the .pst, .ost and .pab files are backed up.  Close Outlook.
 Rename the .pst, .ost, .pab files to something clever.  Restore these
files from the ADSM server.  Start Outlook.  Does it work?

In general, the only way to be sure about the restoration of open files is
to try it yourself.

Kelly