Currently, there seems to be no way in RHN to alter the "Auto Errata Update" setting for an entire group of systems at once: The individual systems all have to have their properties altered individually in this respect. A feature where one could enable/disable the "Auto Errata Update" setting for an entire group of systems at once, instead of having to do this to every system in the group, would probably be useful.
If you have enterprise entitlements, select a few systems and go to: https://rhn.redhat.com/network/systems/ssm/misc/index.pxt At the bottom, select 'Yes' for 'Automatic application of relevant errata'.