The DSC Module and NI OPC Servers are two separate licenses. When installing the DSC module it does ask if you want to install NI OPC Servers as well so I see how it can be confusing.
You only mention that you want to set up an OPC communication so I do want to make sure you understand that, with the DSC module, you can have LabVIEW act as an OPC DA client so if you have an existing DA server you wouldn't necessarily need the NI OPC Server. Also, as of 2017, OPC UA is not included in DSC and has its own separate toolkit.
Matt J | National Instruments | CLA