View of users with the same 'entity reference' field vale
You need two entity references and a contextual filter to accomplish this.

The contextual filter does not use either of the relationships. Just select provide default value, User ID from logged in user.

The first relationship will get you the manager of the currently logged in user: User entity referenced from field_manager

The second relationship will get you the users that have that manager reference: User referencing User from field_manager. Set this relationship to use the other relationship. That's the first dropdown after you create the relationship.

Then you can simply add the User name field to your view and set it to use the second relationship (User referencing User from field_manager).

Any questions let me know. I have this running on a stripped down local install of Drupal 7.