There is no restriction as to who can give feedback for whom. As long as the receiver has access to Employee Success, the feedback will go through. Thus, the receiver can be provider's manager, peer, direct report or anyone. This can also help in setting up a practice where team members are giving feedback to their manager, on a consistent basis.
One important point to be noted here though - just setting a user as feedback receiver does not mean he will be able to see the feedback. Only the users with whom the feedback is 'shared with' will be able to see the feedback.
Common use case is - manager providing feedback about a team member to HR department or his manager & so on.