I would doubt it, since RHEL5 is based on FC6, so you are effectively talking about a downgrade in Fedora terms. There is a thread on LQ somewhere about migrating FC6 to RHEL5 if I recall correctly, but that probably doesn't help a whole lot.
Examples of issues you will have are Firefox, where F8 has version 2.something and CentOS is stil on 1.5.
Rgds
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