This technote should clear anything confusion, if you don't care to sync inherited you don't need ESM on the EV server.
http://support.veritas.com/docs/317725
Details:
Background
The ability to synchronize inherited permissions from the Exchange server to users' archives requires ESM to be installed on the Enterprise Vault server.
Note the following:
1. If ESM is installed on an Enterprise Vault server running 32-bit Windows Server 2003, you can still synchronize inherited permissions from the Exchange server to users' archives.
2. Windows Server 2003 x64 SP2 prevents Exchange Server 2003 ESM from installing, so you cannot synchronize inherited permissions if the Enterprise Vault server uses this operating system.
3. All versions of Enterprise Vault still include the ability to synchronize delegate permissions; that is, permissions set through Active Directory users and computers, or through Outlook folder permissions.
Solution
Microsoft does not support Exchange 2003 ESM on Windows Server 2008 therefore the ability to synchronize inherited permissions from the Exchange Server to the user's archive is not available. Install a supported Operating System on the Enterprise Vault Server.
Related Documents:
276547: Symantec Enterprise Vault (tm) 6.0, 7.0, 2007 and 8.0 Compatibility List (includes Partner products) - Updated March 31st, 2009
http://support.veritas.com/docs/276547