I've found myself in charge of installing some software on an old server running RHEL 5. Unfortunately, since it's just a development server now, it no longer rates a license. I'd like to continue using yum for dependency resolution, etc. My first thought was to just point yum at some CentOS repos, but some googling turned up this instead: migrating from WBEL 3 to CentOS 3. Is this sort of approach my best bet? If so, how much of the migration process is different for my scenario compared to the one in those instructions?
Since CentOS strives to be as compatible as possible, that approach should work just fine. We're converting our RedHat boxes to CentOS as well, and I've simply added the CentOS repos for packages I've needed until I can do a clean move over. Most packages don't check explicitly for RedHat (at least not the ones we've needed). I'd feel safer with a fresh install though if at all possbile.
Otherwise, just follow the CentOS Migration Guide HowTo.
I would highly recommend only doing this as a temporary procedure until you can schedule a time to move to a fresh system though.
Also, make sure you're pointed to the same point release (for yum repos) as what your current RHEL is at. I ran into some odd dependency issues recently which were the result of using the mirror repos on an older point release. Had me confused for a little why things were failing.