Hi,
The AltaVault data interfaces, as well as the management interface, are recommended but not required to be in different subnets or VLANs. Separating them by subnet helps to ensure traffic is targeted to the right interface, but if you have a flat network within your hypervisor don't worry about it. Assign them all to the same is fine, and won't stop the deployment of the virtual appliance.
There is a performance tuning guide available, if you wish to reach out to your NetApp sales rep they can get that over to you. I cannot post this however to the community portal. Sorry.
Regards,
Christopher