This is the closest that Anonymous have come to doing something productive that I've noticed so far. With the mention of non-violence, it's easy to assume that they're maturing on some level philosophically, not that I'd count on that, ever.
In any case, it's quite likely a counter-productive message, and I think it's naive of those posting in this thread to blindly support Anonymous "because they're doing something about it". In any conflict, many potential actions can do more harm than good - this is one of them.
When you want a rebellion, and want it to be successful (and assuming in this case that you say yes to both of these), you don't just tear down one website and declare that "the world stands with" those rebelling against the Syrian Government on that URL. (Especially when "the world" doesn't "stand with" jack - it's like telling them that NATO or the UN can afford to send military aid or something, which they definitely can't do at this point. Sanctions is what the West can afford to do at present and that's all.)
People choose to use websites or not. In Syria, how many of the population do you think would see the website while the hacked version displays? To those reading: how often do you visit your own country's Defence Department website? Not often, I'll wager. And those who are in the military who would use it are unlikely to be as open to so-called "enemy propaganda" as the general populace.
There's a reason why anti-hero rebellion figures often appear on multiple news channels at the same time in their media stunts in fiction - because they have to, to reach the audience figures they need to actually make a difference. It also helps that the regimes an anti-hero goes up against usually have taken full control of the media so it's all centralised. If you tell a tiny portion of the population of Syria to go disobey the government's orders, you're quite likely to get those who listen killed. This is either a lethally dangerous and irresponsible attempt at rebellion, or an incredibly naive/apathetic and inhumane publicity stunt.
There is yet another concern. How many of the people in Anonymous really think about this militarily as a "good time" to encourage a non-violent resistance? I doubt it even crossed their minds if this was good timing or not. A clever resistance is timed properly, especially a non-violent one to a brutal regime. Call me crazy, but I'd say that there is more than one reason why the world hasn't acted against the regime yet. Perhaps Anonymous should have considered such reasons.
So if it was misleading, doesn't reach enough of an audience and is in all probability a badly timed action, how can we consider this a good move for the people of Syria? We should not celebrate the likelihood of someone (possibly an innocent person or even several) getting killed as a result of a premature "rebellion".