Yes. If resource booking (for conference rooms, meetings, etc) is enabled in Exchange, allowing a user to access other users' calendars, the Application Log will record an event 1016 "User A logged on to User B mailbox, and is not the primary Windows NT account on this mailbox" each time a user looks at another users' calendar.
Anti-virus on demand scans & brick level backups of mailboxes will also show the service acount logging on to user mailboxes with event 1016 in the Aplication log.