Actually if you read the comments on the article, you'll notice that a user "iJon" tried it and it didn't work.
The thing is, these instructions are just a hack to install Mac OS 9 from a disk image on the restore CD. This is what you would have to do if you wanted to reinstall MacOS 9 if you have no Mac OS 9 CD, and you don't want to do a complete restore. That's it. It isn't a hack to boot the new Macs into OS9. To do that you'd have to hack the ROM or firmware.