Ghost-Imaging the BOOTCAMP partition for later restore?
I would say you're not on the right track doing an update before you test if your backup works on Windows 7 to Windows 7 first. 

Without knowing what version of OS X and Boot Camp, people might hesitate to report success or failure, but since Apple doesn't "support" Boot Camp you might check with Symantec to make sure you are able to use their support if you need it. 

Are you locked into Boot Camp? It seems you would benefit from having virtual machines you could snapshot and test and co-exist so you don't need to depend on a restore to bare metal scenario.