Hi George, this is possible. We have a very similar setup where multiple domains are connected and sync via gateways to the manager.
You can do this using different user stores on the same gateway or simply just setting up different gateways for each domain but connected to the same manager.
Some things to watch out for:
On the manager, there is a setting that allows the validation regardless of the domain
When you enable the user sync on each gateway, you might have a conflict if there are users with the same user name on both domains... but I'm sure VIP is not the only place you'll have conflicts!!
Other than that... good luck!!