For some inexplicable reason I don't get rhgb the first time I do an install, regardless of install type or source. There are no files left in /etc/gdm/temp that might explain what happens. Subsequent reboots has rhgb launching without a hitch. I don't yet know what is the source, so I'm filing this bug to get it tracked at least.
Any avcs? Try before rebooting chrooting and loading the policy which shows all the dontaudit'd messages (which I don't remember off hand). Could be that rhgb is trying to create something, being denied by selinux and then on subsequent boots, it's already been created. Although I have seen rhgb on live boots (not in kvm but that's a known bug -- but it means I can't verify right now) which makes this a little odd.
Bill found it and is building fixed xorg-x11-xtrans-devel (and rebuilding the xserver against that)
Verified fixed.