On CentOS 5, I run
yum groupinstall "Development Libraries" to install the commonly used development libraries. Can I use the same command on a RHEL5 server with RHN? Is the "Development Libraries" group defined on such a server? Will it break the RHN updates?
Yes, this should still work. I have never installed anything by group like that on our servers, but if you do
You are still pulling the packages from the RHEL repos, so doing group installs won't break RHN compatibility. If you add non-standard repos, you may have difficulties, but pulling everything from RHN by groups is fine.