They have some pretty cool papers on there, but the few landmark papers that Pixar published were all published in the 80s.

Here is a better source for papers (SIGGRAPH, Eurographics and EGSR have the best papers on rendering):

http://kesen.realtimerendering.com/

The Hyperion renderer was made by Disney, not Pixar by the way. Pixar only uses their own RenderMan renderer. Disney uses a mix of Hyperion and RenderMan, as Hyperion is not useable for test renders, as it can take up to 15 minutes until a pixel will appear on the screen, as they trace millions of rays at the same time.