Moshpits are fine. It's a good way to keep the agressive people in one area...and if you spot it just stay way in the front or way to the side or the back. And at roo it's not like a normal venue where if a mosh pit breaks out then everyone is screwed and drug into it because there is so much room...it's those crazy hardcore dancers doing their spin kicks that you have to watch out for...and crowd surfers...they'll get ya.
On a different note...last time I saw OAR (when I got my license 4 years ago) a most pit broke out there. That was the last time I had the desire to go see OAR.