From what I understand if the "Skill" for that App/Device/Service and Alexa are all linked up and the scene is something that Alexa can see, it'll see it and tell you that it has.
With my LIFX lighting the second I complete a Scene in the LIFX app, Alexa blurts out that she discovered a new scene and when I go to the Scene Button in the mobile app it is in the list.