We have configured all The Things Network clusters such that all traffic that is received by gateways connected to a certain v3 cluster will be offered to the Network Server of that same cluster.
Packet Broker does not route NetID 0 (because nobody owns that NetID), so if your gateway is connected to one (v2 or v3) cluster, you will not receive uplinks for DevAddrs 00000000/6 in another cluster.