Admins will need to configure the custom relationship permissions. In the configuration settings, you will have the option to give this custom relationship visibility into private Updates from the point of permission of the employee they have been set to oversee.

Once configured, relationship owners can...

They will have visibility into the Updates the employee has written by going into the user's profile. The Profile can be found under My team.

Note: This gives only visibility after the custom relationship has been assigned. The user will not be able to take action (such as delete, comment, or review) on an Update.