Well for us, our Resource Managers live in Workfront so they see when things change all the time as they are already there.
How do you do unassigned work? Just a job role, a team assignment, or a fake/placeholder person?
For a team assignment, you could put them on the team so that they get those notifications as well as the rest of the team. And if you do just job role or fake/placeholder person, you could a report that just shows those items. You can even do scheduled emails to let them know if there is anything they have outstanding. (i.e. send them an assignment report at noon with any task where role ID is not blank but assigned to ID is blank.)