How can I check for a package service name so that I could use it for 'systemctl enable' on RHEL7.
The easiest way is to simply look at the list of unit files installed by the package, e.g.:
$ rpm -ql openssh-server | grep '\.service'
/usr/lib/systemd/system/sshd-keygen.service
/usr/lib/systemd/system/sshd.service
/usr/lib/systemd/system/sshd@.service