Hmm. Part of the Article seems wrong. While we used Vray for pretty much almost everything in the movie, save for certain effects from Houdini (storm or mantra) for effects like the fireworks, disc, trails/heat, derezzing, etc, I think the CLU head was rendered in mental ray. This is because of the pipeline that was built from Benjamin Buttons which was transferred to Tron.

We did use Vray for vehicles, the world, etc but the one thing I think we used mental ray for was for using DD's custom SSS shader passes setup from Benjamin Buttons. I'll try to verify that if I can.

Good article though. The rest is spot on.