Not true. It's dependent on Data Centers. Venture Co and Ravenholdt are the only RP-PvP realms in their respective Data Centers.
Ah, I see, you're correct.
I don't think there's any chance that Blizzard would put different server types together in a virtual realm, but since they are trying to solve the issue of low population, it leads me to wonder what they would do in the situation that the only other realm types in a data center don't match a low pop server.
I know some CRZ right now are much higher pop than some other server groups even though they do in fact have CRZ.
For instance, my main server, Bleeding Hollow, is CRZ'd with Illidan and Arthas...all three are very high pop. Then I know people with toons on lower pop servers who say even with CRZ they rarely see other people in the world.
It might be a question of how far will Blizzard go to try to "balance" the population on each virtual realm by mixing high and low pop realms.