Short Answer: No you do not need a RemotEye ESS to monitor the SCiB ESS. However, it is recommend that the RemotEye ESS be used to monitor because it it built specifically for the application and allows broader range of interoperability. 

We advise our customers to use the RemotEye ESS for monitoring because it is not limited to Modbus RTU. Customers have the flexibility to use Modbus RTU/TCP IP, BACnet, SNMP, HTTP/s. Monitoring via the RemotEye ESS will allows you to poll up to 100 registers at a time and establish connection via ethernet rather than RS-485.