Not sure about automatic updates, but manual updates should work fine if the people distributing the contrib have setup a yum repository . As an example, take Dungog.net who has a number of contribs available for the SME server. Dungog has a couple of repos, and subject to some additional lines in /etc/yum.conf being added, one can download and install all of dungog's contribs using yum. Same for updates. You can even use cron to check for updates and mail admin when available for download. Yum is just great!