well redhat's official way to do this is to use a "satellite" server which manages your rhel subscriptions and such without having to give all machiens internet access and such. not cheap though. you might prefer to look at maybe using yum on rhel? http://wiki.centos.org/HowTos/Packag...ment/YumOnRHEL
i'm not too familiar with how up2date really works, but i'd image that if you were to persist using up2date, you can still use it against this base server.
apparently rhel5 is now using yum too, maybe losing up2date altogether according to the link there, so maybe this is a better appraoch anyway.