As far as the GTM is concerned, it shouldn't care whether you're load balancing to a Viprion or a set of 8950s, you'd just have to make sure your monitors and configs are changed accordingly. But yes, assuming you get the same config set up on the Viprion there's no reason you shouldn't be able to have GTM balance traffic to both data centers still.
You wouldn't be able to make the Viprion an HA partner with the 8950s in the other DataCenter, because it wouldn't have an identical config (I assume), but if it's running independently and being balanced traffic by GTM, that should work.
Colin
Nimbostratus