YouTube - Referee gets decked by Vikings guy
Looks to me like Dugan was running down the field looking for someone to block (most likely #31 who is shown chasing Harvin toward the end) and just didn't see the shorter official or assumed he would get out of the way. Looked like a case of a big beefy dude hustling to make a play. He had tunnel vision, didn't see the official. It was clearly by accident.
Anyone who has been a BJ or U is fully aware that any player who is not a running back is not looking out for the officials. Their brains are going a mile a minute and if you don't get out of their way you could be collateral damage.
Cowherd is a bonehead.