If hosts of VMs in your environment are not configured in compliance with the vSphere Hardening Guide, you will receive an alert notification. Alerts are triggered when settings or properties are not in compliance. Alert-based compliance is not activated by default. You have to override and enable at least one of two policy settings. One is for alerts related to hosts, and one is for VMs.
It is worth noticing that since vSphere 6.5, it is no longer called a Security Hardening Guide, but a Security Configuration Guide. Unfortunately, at the time of writing this book, there is no vRealize Operations management pack available for download at VMware Marketplace's site to enable vRealize Operations 6.6 to monitor vSphere 6.5 for security configuration compliance.