AFAIK, on a default RHEL installation the wheel group does not serve any purpose.
But you can put some PAM changes into place to make RHEL behave like a BSD system would with the wheel group. Upon making these changes, only users in the wheel group are able to use su
to get root access.
I wrote a howto long ago on this topic (on a SuSE forum, back when it was called SuSE). Maybe someone can dig something up for you if you're interested.