Outlook doesn't currently use the Accept/Decline, and mounting a mailbox in Outlook doesn't mount it in ZWC.
If you do mount it in ZWC, then if you have the right screen elements enabled (look in the View menu if I recall correctly), Outlook will flash and let you mount the share via a button-click.
See bug
Bug 30465 - ZCO recognize and add share to Outlook and the bugs referenced in the comments. Some work has been done toward improving Outlook share recognition but there's still more to be done.