Judging from the site, I'm guessing that he's just encoding the existing TV-fansubs into mpg/DVD format. The fact that all the subs are hardsubs is a giveaway. So I doubt that ripping the .isos and re-encoding to .mkv would provide any quality gain. It'd be like taking a CD that somebody made by burning .mp3s and re-ripping .mp3s out of it.