Are you talking about the default community used for /devices (infraestructure, click on "devices", details, configuration properties, scroll down to the comunity), which is what zenoss uses for devices where you do not define the community when you model, or something else

Each node might have that defined differently, or even each device, depending on what you did when you discovered them or added them.

On the other hand, i think that if devices send traps, zenoss picks them regardless of the community.