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
[*] 
https://fedoraproject.org/wiki/EPEL/epel7