Yes, you can copy the anymixPro.vst3 file from the Nuendo VST3 folder to the VST3 folder in Cubase (for example) and it will actually appear on the list of available plug-ins but when you try to load it you will receive an eLicenser Control Center license error.
Even though you have a Nuendo 6 license.
Yes, like with any other third party plug-in. On the other hand the licensing system for the retail version of Anymix is iLok. The retail version should not interfere when loading Anymix inside of Nuendo.
And if you run it outside of Nuendo it will search for a license on an iLok and not on an elicenser.