Once you have configured the custom relationship permissions, you will have the ability to give this custom relationship visibility into private Feedback of the employee they have been set to oversee.
To view this, the person who has been given this visibility and applied this custom relationship, can go to the "You" page of the user they now have visibility into.
Here, they will be able to see any Feedback (private and public) this employee has been given.
As a reminder, this gives only visibility. The user will not be able to take action (such as delete) a piece of Feedback.