Well, I don't run Heretic 2 but I do run Quake 2 and the solution is that the OpenGL lib in the directory you listed is a standard X11R6 lib but Nvidia has their own for their cards. I assume you have loaded the Nvidia driver ( to check use rpm -q NVIDIA_kernel )
So, try moving the /usr/local/games/Loki_Demos/demos/heretic2_demo/gl_drivers/libGL.so out of the way (rename it to say libGL.so_original) and make a symbolic link from /usr/lib/libGL.so to /usr/local/......./libGL.so . So when the game calls it's own lib it actually points to the Nvidia system libGL !
Not to be insulting but here are some more explicit instructions.
1)Check to see that libGL.so is in /usr/lib
ls -l /usr/lib/libGL.so
2) If so, then
mv libGL.so libGL.so_original (as root user)
ln -s /usr/lib/libGL.so libGL.so (as root user)
3) run the game and see if it works ;-)
I noticed that in your listing you were running as the root user. It's best not to run as root but as a regular user. Security and reduced risk of "messing" things up.