Is there no way to exclude your WHD monitored inbox from the dynamic distribution group, like move it to a different OU?
Another thought might be to configure a rule in your WHD monitored inbox to auto-delete messages sent by 'allstaff', or at least redirect them to a folder other than the inbox. This way, WHD won't pick it up and create a ticket.
I ended up changing my DDL from all exchange mailboxes to pulling from a tag in the Company Field. Thanks for the hint, that pulled me in the proper direction.