The OPC-UA server provided by Ignition is in itself modular, and supports extension through the Driver API system. With the API, you can create new drivers that pull data from any source, and expose it through OPC-UA, without having to worry about any of the details of the OPC-UA specification. Any compliant OPC-UA client will then be able to consume the data that you provide. 
The process of developing a driver can be somewhat involved, but there are a variety of useful base classes that cover the most common scenarios. Furthermore, the Modbus driver developed by Inductive Automation has been fully open-sourced, and can be referenced as a model for creating device-based TCP/IP drivers.