When using vSAN 6.6 it is possible that the health check is unable to verify the controller firmware and returns only "NA"
The firmware check relies on vendor specific tools (such as "perccli" on Dell or LSI storcli). Please contact the hardware vendor to get the correct RAID utility for the system.
If the correct utility details are available and there is no need to ask the vendor, please use the KB to download and install it:
vSAN Health Service - Online Health - Controller Utility is Installed on Host : For vSphere 6.7 and earlier versions
Note: There is no impact as long as a supported driver / firmware combination is installed. This can still be verified manually.