Sometimes I have relinked after OS updates, and for several years I have not. Generally, I would only recommend doing a full relink for sure if upgrading from one OS version to a new one. Minor updates on the same OS version, like OEL 6 do not require full relinks.
It depends on many factors . I couldn't see oracle mentions this as mandatory.
How often OS team perform these kind of activities, i believe there is specific time for update.
If you environment allows downtown its ok to do it following their update.
If its quiet often happening i would schedule re linking quarterly,every 6 months, unless update does not break running application.