In addition to the standard RHEL base repositories please ensure the following repositories are also enabled.
[rhel-7-server-extras-rpms] name = Red Hat Enterprise Linux 7 Server - Extras (RPMs)
[rhel-7-server-optional-rpms] name = Red Hat Enterprise Linux 7 Server - Optional (RPMs)
Those are actually EPEL7 deps[*] and RDO depends on EPEL. I've updated "NOTE for RHN users" in https://fedoraproject.org/wiki/EPEL#How_can_I_use_these_extra_packages.3F to mention required RHEL7 repos.
Cheers, Alan
epel-devel@lists.fedoraproject.org