I dunno, I would suspect that it will assimilate EZD1. I can't see how it can help doing that unless they have a small sample set that is roped off. Keep in mind that if you have legacy projects that use EZD1 in SONAR, you will have problems with the inputs of your other softsynths being assigned the outputs of EZD2. I don't know for a fact but I have a hunch that when you uninstall EZD2 and go back to EZD1 the behavior will clear up.
If it was me, I would question Toontrack staff about this in their Sales inquiries area of their forum before using it with SONAR and not demo the product until you have a definite answer.