Please read the article that i have written on SNAC.
SNAC can be integrated with SEP but it can be used as a Stand alone application as well.
It will work with Trend Micro Office Scan and other AV 's that's there in the article.
You can purchase SNAC only license and deploy SNAC only clients. IT does HI checks with many other AV/Aspy/andFirewall Products.
NO need to migrate to SEP in order to use SNAC however SNAC works better with SEP.
http://www.symantec.com/connect/articles/what-all-can-you-do-symantec-network-access-control
Do read this article and lt me know if there is anything else i can help you with.