The backside of the model that is bolted together also had a grey patch for the 3G antenna on the back, instead of the black. So clearly there were a few versions of working iPads around that we haven't seen, as if one had a camera I guess we'll wait and see.
I'm gunna say a big no on this. There are plenty of similar looking marks all over that iPad, but the one with the arrow happens to be approx. where you would expect to find a camera. Why would it only show up once, they used the same iPad throughout the keynote didn't they?