According to the help when you add a hibernate descriptor an entry should appear below in the Session Factory after you click apply.
Hibernate: when a Hibernate configuration descriptor is created, click Apply. After that, an entry with the descriptor name is added to the Session Factory column.
I can only get it to appear after clicking OK (which exits the screen), then going back into the projects settings and into this page.
Not appearing after clicking apply gives the impression that it isn't working (it was a coincidence that I looked again after clicking OK).
The help should be modified or the functionality should reflect the help.