Spacewalk has been installed, runs and can be accessed. The expectation was that installing Spacewalk was sufficient in order to run rhn_register.
[vagrant@localhost ~]$ sudo rhn_register
sudo: rhn_register: command not found
The idea was that there would be a rhn_register package.
[vagrant@localhost ~]$ sudo yum install rhn_register
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.1000mbps.com
* epel: nl.mirror.eurid.eu
* extras: mirror.netrouting.net
* jpackage-generic: sunsite.informatik.rwth-aachen.de
* updates: mirror.netrouting.net
No package rhn_register available.
Error: Nothing to do
Googling install rhn_register did not help to solve the issue.