HI,
SEPM 12.1 are supported Below Platform.
Support for additional operating systems
Symantec Endpoint Protection Manager (SEPM) now supports the following operating systems:
■ VMware Workstation 7.0 or later
■ VMware ESXi 4.0.x
■ VMware ESX 4.0.x
■ VMware Server 2.0.1
■ Citrix Xenserver 5.1
What's New in Symantec Endpoint Protection version 12.1
https://www-secure.symantec.com/connect/articles/whats-new-symantec-endpoint-protection-version-121
Check this thread
https://www-secure.symantec.com/connect/forums/sep-12-support-esx-andor-esxi