The hub does not check that it can communicate with all of the robots. It just generates an alarm when a robot has not checked in recently. (Recently means it has been 1.5x the check-in interval of that robot since the last check-in.) If robots can open connections to the hub but not vice versa, the system will not alert you to that at all. You'll only find out when you try to configure a probe. Or if you've setup something else, as mentioned by Philip below. The good news is that you'll still get alarms and QoS from the robot because it can connect to the hub, so your monitoring is not impaired--at least not until you want to change it in some way.