Hi,
I'm sorry to say that you are bound to run into trouble one way or the other with this setup, if you ask me.
First off: I'd never virtualize all my DC's. Always keep one physical to mitigate any problems with your virtual infrastructure.
Second: NEVER, and I mean NEVER use snapshots of any kind to restore a DC! It's not just against Microsofts recommendations, it's also simply a very bad idea. You could get into a world of hurt if you try to restore a DC from a snapshot.
Third: in my experience NetApp snapshots (SMVI) with or without(!) taking a VMware-snapshot works pretty well on all servers. That is, if you want to backup the OS and static data. To backup active (often open) data like databases (such as an AD!), you'll always need some sort of agent, being it SMSQL, SMO or a traditional backup agent. In your case you should definitely use a traditional backup agent.
Hope this helps.
Regards, Bjorn