Recovery Manager can register the Public Folder Hierarchy, but when you try to open it once it is registered, you get Unknown Error 0x80040119, and it will not open.
This is by design.
Recovery Manager only uses target registration for restoring to the target. It is not used as a viewer in any way when dealing with Public Folders. RME does not have the API's needed for viewing the Public Folder Hierarchy.
The registration of the target is still valid, and you can still restore to the target by opening up the source public folders and choosing to restore to the registered target.