Lossless VOB conversion with ffmpeg

If you mean you want to change a container, that is a VOB to MP4 or MKV without changing hte codec (MPEG2 to H.264, let's say), then yes, it can be done losslessly as follows:

ffmpeg -i your_VOB_file.VOB -c:v copy -c:a copy output.mp4

MKVToolNix can easily make an MKV out of a VOB. Of course this isn't using ffmpeg (directly? - this kind of stuff is a mystery to me), but it may help you accomplish what you're trying to do.