Are you talking about this announcement? I don't see any reference to a plug-in, just integration. If there's another announcement that talks about a plug-in, please post a link with specific details.
If that is the announcement you meant, as Brian81 mentioned above, the Installation and Administration Guide's Chapter 29 is loaded with information, such as (from p 669):
A vShield-enabled Shared Insight Cache runs in a Symantec Endpoint Protection Security Virtual Appliance. You must install the appliance so that Windows-based Guest Virtual Machines (GVMs) can use VMware vShield Endpoint to access the Shared Insight Cache.
That seems to indicate to me that a Security Virtual Appliance is indeed required. Did this (from Chapter 29) not answer your question? If it did answer your question, you should mark his post as the solution.
sandra