Ignoring the compiler mismatch is a bad idea, especially since he is running a relatively old version of RH. Things are likely to break if you are using a kernel build with compiler A and kernel modules build with compiler B.
Before trying to run the nvidia installer build a new kernel and kernel modules with whatever compiler you have installed. Install and boot this new kernel (make sure to keep the current kernel available in case the new one doesn't work). Then run the nvidia installer again which should then work.