Yes, replicate the remote copy.
You could do the same with SQL, however, you should at least apply some sort of snapshot mechanism to protect against data corruption and stuff.
Also, you would have to break the mirror for upgrading EV:
http://seer.entsupport.symantec.com/docs/313452.htm
There might be additional steps necessary to promote the secondary mirror as primary:
https://www-secure.symantec.com/connect/forums/support-sql-database-mirroring-sql-2005-sp1
You might want to contact symantec support to inquire about other potential "issues" with SQL Mirroring.
(I haven't used it myself yet)
Cheers
Michel