I have 5 difference vCenter servers installed over various timeframes and I am seeing different counts for the Non-Critical Host Updates across them. After some digging it appears that this is due to the Nexus 1000v updates.
We have not deployed the Nexus to production yet so this was a little confusing for me. It appears that when Update Manager is installed it downloaded the patches for the Nexus 1000v, but they are not included in the updates that are downloaded because we have none running in the environment and Update Manager was not configured to download them.
For consistency across my environments I have enabled the custom patch download source for Cisco. The URL ends in csco-main-index.xml. This does not change functionality for our deployment, but it quiets the gnawing thought that we are applying different patches to our environments.