Prior to Pro Tools 12, I had been using Pro Tools 9 without support for AAX plugins. I would always see Vienna Ensemble Pro and Vienna Ensemble Surround as plugins in Pro Tools.
After upgrading to PT 12, I only see the Vienna Ensemble Pro. I really don't know how PT 12 decides to show the VST2, VST3, RTAS, and AAX plugins if they're all installed, but I don't see the Vienna Surround plugin.
I'm sure it wasn't removed, so I'm not understanding why it's now missing...