I can clear this up. First, struckn is one of the most knowledgable members I've come across since I came over here. He has yet to pass information that I, or anyone else, has had to come behind and correct or update. So to set the record straight, installing the official 4.3 OTA MK5 build either OTA or Kies will definitely install the Knox Bootloader on your phone, forever, or until someone figures out how to get rid of it, but from what some guys way smarter than me have told me, that isn't happending anytime soon. Secondly, you can absolutely root your phone if you have the Knox bootloader. Just like any other rooting process, you flash the CWM of choice via Odin first. But unlike other builds, doing so with this bootloader will trip the Knox "count" and you're warranty is now voided, but you'll have CWM, which you can then flash the zip file of SuperSu Update 1.8.0 and voila, you have root. I have only had success using Philz Touch Recovery to get Super Su to stick. CWM did not work for me. Here's the link to both recovery and SuperSu, if you're interested. Enjoy, and good luck.
Note: This has been confirmed for the Sprint/VM/Boost versions of the SIII. Make sure you read and search if you have a version other than SPH-L710
Recovery:
http://androidforums.com/boost-mobi...cial-philz-touch-recovery-6-0-11-24-13-a.html
SuperSu:
SuperSU Download