We monitor Automation Direct’s ProtosX IO over ModbusTCP on freezers. It works great! If the freezer gets too hot, Ignition alarms and sends out emails. No PLC required since it is not controlling anything. You do have to toggle a bit in the configuration to not timeout on the Protos IO otherwise if the Ethernet disconnects and times out it will not reconnect.
We also monitor 20 J type thermocouples this way for profiling heater platens over WiFi so the calibration tech does not need to find a network port to plug into. The IO head unit support hundreds of IO. You could do the same with WAGO, Beckhoff(they make ProtosX), OMRON, etc…
I have found that when skipping the PLC, Modbus TCP works better than Ethernet/IP since you get both master and slave protocols with the Modbus driver. The Ethernet/IP driver is intended to talk to PLCs and retrieve variables and not talk to IO. Modbus is an older simple protocol that does not care what it talks to. Mapping can be a headache however. The Protos setup tool helps with the mapping.
The MOXA IOTHINX4510 specs say that it will talk Modbus TCP. Its strange that it would not talk.