The exchange jorunal process only sends a copy of SMTP email it is not designed to journal calendar items because calendar items are not handeled by the MTA which is the service that sends the duplicate email to the journal mailbox
EV should just archive them regardless. EV actually archives all folders in the journal mailbox albeit mostly it's just going to be the Inbox that contains items. Perhaps the calendar folder has been marked do not archive somehow,or perhaps nothing is getting archived from the journal mailbox??