I've used the instructions at http://wiki.centos.org/HowTos/MigrationGuide to move an RHEL system to CentOS with reasonable results. Of course, YMMV. It sounds like you have the added complication of a virtual-to-physical, I can't say much about that as it is not something I have done. Physical-to-virtual (w VMware) yes, but not v2p.
Good luck!