Nero does a check that the associated vob files are there and also that there are no additional ones that is not referenced in the VIDEO_TS.IFO file. That's why you get the 'reallocation error' in Nero. ImgBurn only does a 'Get VTS sectors' and only fails if here is a .ifo/.bup file missing and not if there are missing .vob files or additional ones, as in your example.
On some DVDs there are dummy/fake menu vobs like in this case, the VIDEO_TS.VOB. The reason might be to get the bup and ifo version of the VIDEO_TS to be placed in different sectors opposite of each other on the disc surface to avoid a scratch on the disc that makes it impossible to read both of them. If you get a scratch on one side of the disc - the other side should be fine and the other VIDEO_TS file can then be read by your reader/player and the disc is then not totally useless. Some movie studios also put a huge fake menu vob file on the disc to make it harder to get a decent compression out of the DVD.
In this case, the VIDEO_TS.VOB file can be deleted without issues.
ImgBurn uses the 32K padding option to avoid this 'scratch' scenario.
From the guide section: