I guess you've restored from SME8. This problem has been fixed, but not pushed to the mirror yet. I need to do this ASAP. Waiting for this, you update smeserver-support from smetest:
yum --enablerepo=smetest update smeserver-support
Finish with a post-upgrade and a reboot, and you should be able to install openssl-devel (even if I wouldn't recommand installing *-devel stuff on prod server)