Kalen,
I agree that the tree is damning, however I'm afraid that the elevation evidence you posted for it being #6 actually makes a good case against it.
The 5th fairway sits at 250-256 ft elevation, and the 6th green is at 220-228 ft. Given how the photograph is composed, on first glance I might be able to accept that the background area you believe is the 5th fairway is 25 ft higher than the area that you think is the 6th, but looking at it more closely, the shot is definitely downhill, and given all of the space that is between the two areas (after all, the trees do not sprout up from the greens edge: there is definitely foreshortening) I can not accept that the background grassy area is higher than that in the foreground.
It's much easier for me to believe that we are discounting a tree or one has been removed than for the elevation to have changed that much.
One new wrinkle to add: there is space and grass behind the row of trees on the right that makes 0 sense if it were 5,6, and 7, but fits perfectly as the beginning of 18's fairway.