Have you taken a look at the below article?
http://www.symantec.com/docs/HOWTO101709
Essentially it walks you through the Management Server upgrade but says nothing about the clients other than that the v11 SEEMS support communications and management of earlier clients. I get the impression the idea is that as you won't have to change anything on the client machines, you should be able to avoid decrypting them.
Unfortunately, your specific version of SEE is not on the list of supported older clients according to the below article:
http://www.symantec.com/docs/TECH153772
With no documented guidance on if SEE7.0.5 clients can be directly upgraded to v11 software, I can only see 2 options for you:
- Give it a go on a test machine and hope for the best
- Upgrade to an older SEE version that is supported for management by the v11 SEEMS, and that allows in-place upgrades without decryption
Option 2 would be safest (and supported) way forward. Just FYI, to support this, take a look at the below article about upgrading machines to the v8.*.* client software:
http://www.symantec.com/docs/TECH193044