*UPDATE - 8/1/2013*
Yep, it worked. It did require me to log out of OS X - I chose to reboot, so had to wait until I had a window in which I could shut down VMware, browser, Notes etc.
However, now when I run: -
$ ssh -X wasadmin@rhel6
I see a short delay whilst XQuartz kicks off, and I get an icon: -
in the dock.
More importantly, I can then run X11 commands such as xev and see the results back on the Mac's desktop. Which is nice :-)