The correct answer would be: It depends! 😊
As long as you want to use the full ("built-in") version of MIR Pro in Vienna Ensemble Pro (... the one that is able to do all the nice stuff automatically, like guessing Instrument Profiles, adding MIR instances to new channels, MIRx preset handling etc.), you will indeed have to use a separate instance of MIR Pro in each frame.
But there's a little-known work-around: If you decide that you can live without all those intelligent features which let MIR "talk" to Vienna Instruments as well as to Vienna Ensemble, you could use the conventional VST/AU plug-in version of MIR Pro. All instances will share one common Venue View then. You will get the same results sound-wise, but this method might need more manual input from your side.
I'll add two screenshots to this message, to make it clear what I'm talking about. 😊
In case you're not familiar with the differences between "full version" and plug-in version, please take a look at the add-on to MIR Pro's manual which covers these topics.
HTH,
/Dietz - Vienna Symphonic Library