So after seeing this post, I contacted the ADN, since the company I work for is a member of the ADN,
and I STILL was not able to get those header files from them.
Apparently they are still considered proprietary. They recommed, surprisingly, not to begin my project in GLSL but in Cg.
However, I pointed out to them that Cg is no longer supported by nVidia, and nVidia itself recommends not to implement new projects in Cg. I have not yet heard back any reponse on this.
Just thought I'd point this out. I would be interested in anyone who has successfully written a GLSL implementation to work with viewport 2.0 in maya, just to see what pitfalls they ran across, and if they were ultimately successful.