Good point, I remember hitting that too. It was easy to solve though, I just had to edit the mlnx_add_kernel_support.sh script to accept CentOS 6.4, at which point it then runs through fine and does everything it needs to.
Editing the script is simple. Use vi or something, and look for strings about "6.3". Add one for 6.4, and have it think its running on rhel6.3.
That should work fine. (in theory)