We are using VeeamBackup for backing up all of our virtual infrastructure. Up for now we didn't have virtual DC's but when you introduced SureBackup I started to plan a migration. What I noticed was one post from Gostev:
Hello Sam, if you have multiple domain controllers that restoring one of them in the isolated network would not work correctly. Domain Controller needs to get in sync with other DCs including FSMO roles holders as a part of restore process.
Sam, yes you will be able to use SureBackup to access Exchange as long as you use backup of Domain Controller with Global Catalog for your SureBackup Exchange application group. I assume you have GC in your site. Presence of FSMO role holders in the test lab will not be required. Thanks.