Index rock is seperate from the knifes edge. It is just a very distinct rock on the side of the trail on the way down from Pamola peak to Chimney pond. Many folks have discovered that it is a lot easy to climb up on then to climb down off of.
Knife Edge does seem to be just that. It's like hiking across a humongous pile of boulders. I've enjoyed hiking that section of trail more than any other. Check it out sometime, if you ever get the chance and feel you're up to it and don't get vertigo too bad.