I'm sure a lot of the updates do not really apply to all setups, but i don't think update manager cares about that.
It only sees an update package for the configured version(s) of ESX, and does no checking on whether it applies to your ESX host or not.
So any update it downloads will be added to the baseline (if it's dynamic)
A scan will just compare the installed packages with the baseline, again without checking whether the contents of the packages actually apply to the scanned hosts.
Scanning will just change the status of the host in Update Manager to non-compliant (make UM aware of the non-compliance)
The moment any package gets downloaded and added to the baseline, your host will become non-compliant, although UM won't know it without scanning.
If your baseline is not dynamic, even a scheduled scan will not make the hosts non-compliant, because you have to manually add the updates to the baseline first.
So either way, getting a notification when new updates are downloaded should be enough.
The only way to really test this is creating a new baseline with drivers that do not apply to your hosts, and seeing if a scan will make your hosts non-compliant to this baseline. (this should be done on a clean installation, otherwise the updated drivers may well be installed already)
