Hello,
I agree, I would recommend you for both the servers to download the update and not to replicate the content between sites.
If you configure sites on your network for replication from another site, the content updates that are in the database of the primary site will replicate as part of the database. In this case, you only need to configure updates on the primary site.
If you choose to use product updates as well as content updates, you should not replicate product updates between sites, because these updates can be quite large, and one exists for every language that you select.
If you decide to replicate client packages and LiveUpdate content, you may duplicate a large volume of data. Should you replicate many packages, the data may be as large as 5 GB.
Check this Image:
Reference:
Replicating client packages and LiveUpdate content
http://www.symantec.com/docs/HOWTO27204
How to update virus definitions and other content with Symantec Endpoint Protection and Symantec Network Access Control http://www.symantec.com/docs/TECH102467
and
https://www-secure.symantec.com/connect/articles/replication-and-considerations
Hope that helps!!