Are you placing the background media on a video track beneath the keyed video track? If not, you need to.
Yes, I have tried both ways and neither is working.
Place the background (the scene that will be revealed where the green is) on V1.
Place the green screen scene on V2 directly above the background clip.
Apply the Ultra Key to the clip on V2. If it removes the green portion of the clip, it should reveal the clip on V1 in those sections.
It doesn't matter which specific track the media is on, provided that the material to be keyed is directly above the reveal media.
Have you selected the key colour with the eye dropper (effects control) and ensured that the track eye icon is not disabled (a line through it)?