If VMware-ESXi-6.0.0-Update3-9313334-HPE-preGen9-600.9.8.5.4-Sep2018.iso is used to new install a new host, does it still need ESXi600-201511001.zip ?
The patch appears to be needed for kb2136854:
https://kb.vmware.com/s/article/2136854
Normally I would assume such patches too old to apply to a late iso build, but it was mentioned for the current release of Backup Exec:
You'll see this mentioned when you search for KB 2137545, 2136854.
Perhaps Veritas mentions it in case a host is using a really old build from 2015?