What is the best solution for an industrial network containing SCADA, OPC servers and PLC’s. use a Domain or just place the servers into a workgroup?

just place the servers into a workgroup, because Scada specializes in the compelling visualization of real-time data and has produced exceptional data visualization solutions for manufacturing, power & utilities, automation

Supervisory Control And Data Acquisition, this type of software using big production industries the right information getting the employees the right time it will improve the product quality and maximize the production.

It should be tackled under technical way out.

its better to have Modbus TCP over IP with Ethernet Media. For opc like Kepware u can use, Modbus tcp module can be use at plc end or if plc(like compact logix) if u have ethernet port than no need modbus too. use only ethernet. that it.