People make too much of stuff like this. If you're the #1 team in the entire NHL in SA, you're only about 3 or 4 shots per game better than the NHL Mean. It's the quality of the shots you allow that's far more impactful. Or, in the Devils case, it's the fact that the "system" is so risky it results in almost 1 guaranteed fender-bender per night, often several more.
Well the deviation from the mean is one thing, say 3-4 shots in this case, but the difference between the Devils and the worst teams in the league is over 6 shots per 60(it's late so I'm not looking up the per game stats). So night after night the worst teams are averaging 36 shot per game against while the Devils are a little under 30. That is significant. Certainly not indicative of a coach who only cares about offense.
Now are there risky elements to Hynes system? I can see more of an argument here. And risky is maybe not the best description, demanding might be a better term, but even then, Greene doesn't seem to fall victim to these issues as much as Sev's or Subban. Or Butcher who is certainly more on the skilled side of the d-man spectrum, he's not making these blatant errors at the rates of other guys, so there is an execution portion of this equation.
End of the day I think Hynes gives guys freedom, he welcomes players who are willing to push the puck ice, but he does not demand it and is actually willing to play guys who play a much more conservative game.