First off, what application are you using?
DVD to DVD ?
Please explain in detail, what version you're using (please don't say the latest, specify the version) and exactly what steps you're going through.
Fab should not be creating just .vob files unless you're using DVD to Mobile.
DVD to DVD will either create VIDEO_TS and AUDIO_TS FOLDERS or >.ISO files. Both these formats will contain .IFO, .BUP and .VOB files.
With respect to the burn engine...what happens if you navigate to
Common Settings > Write > Burning Engine
Does it not allow you to select from VSO, Img and Nero as options?