I'm one of those who need this feature, be in touch about updates, it is a mandatory, no more, no less. If you don't have installed contribs on your server, you won't receive emails, if you have installed contribs and if updates are available, then you will receive an email with a daily or weekly or monthly frequency.
If you decide to not apply security updates to your customers, please reconsiders your behaviour...it is the same if you don't want to apply updates in the core....
If you have some custom rpms I see several solutions
-bump a number of rpm superior than those of smecontribs and you will have peace
-share your modifications and import them in smecontribs (better idea)
-do a custom template (bad idea)
-ask and propose code in bugzilla to disable the option in bugzilla (worse idea)