There is no Component for "rhn_register". When you've registered, you're dropped out of the app and told (if you bother to read it), to visit www.redhat.com. Then you need to locate the RHN Icon, login, and you're told you have new updates. At no point does it give you a clue that you need to run the "up2date" app. When you've registered successfully for RHN it should run up2date for you on exit.
the next version of rhn_register will describe how to access Update Agent.