After doing a little more research, it appears he did indeed get his knee down. Can't really see that from the broadcast angle.
I still say, as does my original post, the blame should be shared with the officials and the offense, though. If the offense was truly well-versed and practiced in the end-of-game scenario of downing the ball in the center, spiking the ball, and marching the field goal unit on to the field (a scenario I know teams typically practice to be completed within 10 seconds), they should have been at the line and ready to snap. They are standing around. No sense of urgency.
The officials should have acted quicker, as well, knowing this was the end-game scenario that Wisconsin was trying to accomplish. All-around, it's a colossal fuck-up.