To put it short, it's not possible.
A bit more detailed, as I tried it for over a year, RHEL6 is missing several requirements for 3D. First of all the Kernel, 3.2 (as far as I remember) is minimum, then comes Mesa 8 with several compile flags enabled and then also comes the actual 3D driver (vmwglx).
If you satisfie all those requirements, you are actually able to enable 3d, but sadly it's only an emulated form. Your GPU will never get any load (at least not in my testing). This is why I now finally switched to Linux Mint (Debian based) where it's working out of the box.
3D might start to work with RHEL7, but that probably takes an other year until it's released.