When an eNodeB is going to be shared with multiple operator core network, it means eNodeB is going to make S1-Setup with each MME of different operators. As per my knowledge each MME support one or more tracking areas. In S1-setup request, an eNodeB sends "Supported TAs". Since an eNodeB may have multi-cell support, Supported TAs IE can be a list of tracking areas.
MME matches the received TAs from eNodeB against the configured ones and based on that MME responds to eNodeB.
It means each operator's MME should have support of same tracking area code if we consider one eNodeB which is going to be shared among different operator has only one cell and one cell can broadcast only 1 tracking area. Each operator PLMN would be broadcast in same cell and each cell can broadcast up to 6 PLMNs (one primary and other plmns would be considered as secondary).
In essence, what I think is only common tracking area is pre-requisite to implement MOCN.
I am waiting for others to respond to correct me if I am wrong and enhance my knowledge.