Fab is not designed to re-author or to handle video content that does not conform to dvd video compliant structure.
I've tried this a few times with Fab and it is a hit or miss...usually miss process. Img will work just fine.
Simply burn the Img "built" files with Img.
Img should have no problem with this, but if you do run into a problem, simply run the files in Img's Build mode.
If necessary, this should only take a minute or two.