I don't recommend doing this. I followed those instructions to the letter, and got a completely broken Nexus 7. I somehow managed to recover enough to reinstall the factory image, but it took many many iterations and blind shots in the dark, consuming several hours of my time.
More anecdata: I've done it on two or three devices without issue.
I thought the factory image install scripts rewrote the partition table, so even if you screw it up it should come back as long as you still have fastboot? Or maybe I'm thinking of another model.