RHN uses up2date for 4.x and lower. It uses yum for 5.x and higher. It is not an "easy" tool to use, and I wonder why you would not want to consider ZLM as an option, as RHN will cost you significantly more money. RHN Satellite is NOT free.

Also, SMT is not an update tool. It is a portal. The issue is that Novell Zenworks Linux Management is a true tool to manage your updates. If you just want a portal to go to and do it relatively manually, then SMT or RHN would work.

If you want to go to a central place and manage the updates for all your machines, ZLM or RHN SATELLITE would be the option, however ZLM will work for both, at a nominal cost, and RHN Satellite is expensive.