What Snowden confirmed was more the scale. The details honestly shouldn't have been terribly surprising for anyone who had followed computer news for the last decade, unfortunately.
As far as Russia hacking the DNC is concerned, what I know is there are several cybersecurity companies that have confirmed that Russian hackers were involved, publishing white papers with a fair bit of evidence. I personally haven't seen a single cybersecurity company so far refute that information.
I do welcome a technical refutation of the white papers or a point to a cybersecurity company that disagrees! Counterpoints however have to be data-oriented to be interesting. I consider random commentators posturing that all this is just US propaganda with little evidence to be merely cheerleading, sorry, that's not interesting to me...