Hi,
Thank you for posting in Symantec community.
I would glad to answer your query.
Q.My main purpose of installing it is for me to install Symantec Management Platform and IT Analytics for SEP which have a separte SQL Server, so do I still need to install SQL Server on the server where I will install Symantec Installation Manager?
--> No, it's not mandatory to install SQL server and SEPM on the same machine.
If SQL is on remote machine then install of SQL native client on the SEPM machine is mandatory.
While installing SEPM you will have to choose either of the database, Embedded OR SQL.
Check these article to know more about it.
SEPM 12.1 Fresh install with Embedded database - graphical overview
https://www-secure.symantec.com/connect/articles/sep-121-fresh-installation-graphical-overview
SEPM 12.1 Fresh install with SQL database - graphical overview
https://www-secure.symantec.com/connect/articles/sepm-121-fresh-installation-sql-database-graphical-overview