No, the ADEX footprint feature is not related to building footprint data, it just looks at existing models and figures out their shape. It isn't much help with autogen, I guess, although I only use ADEX for airport facilities.
I've spent an hour doing a wee test on how quick it is to get photoscenery into the simulator. I chose Ashburton because it was mentioned here:)
An hour ago, my Ashburton looked like this in Prepar3d:
Now it looks like this:
That's 6862 buildings and 1597 vegetation polys.
I wouldn't release it like this, as there's plenty of work to do first, like colour-correction, water-masking, adding trees etc, but this is a good start.
Here are the steps I took:
At 1:45 I ordered the download from LINZ, for the aerial image, footprint data and vegetation data.
At 2:08 LINZ emailed me with a download link
I then downloaded the files, and by 2:15 they were unzipped
At 2:25 I dropped the aerials into resample.exe, after piecing them together and building a geoTiff
While that was running -- it takes time, in this case about 20 minutes -- I ran Scenproc and converted the LINZ footprints/vegetation data into autogen
By 2:45 I'd loaded it all into Prepar3d.