I have an application where I am communicating with a PLC over OPC. I used this tutorial here:
For deploying an EXE using this setup, what exactly do I need? Do I need the DSC Run-Time and OPC Servers? Its not really clear, and I want to make sure I dont spend more money than I need to as OPC servers is a little pricey.
This should answer your questions:
Using and Deploying NI OPC Servers, DSC, and LabVIEW OPC UA Toolkit
If you're following that tutorial, you shouldn't need the OPC UA API. If you decide to use it, note that it is included in LabVIEW DSC before LabVIEW 2017, but is in its own dedicated Toolkit in LabVIEW 2017/2018.