Hi Till,
there is a framework in NW-layer that could be used to read data from data sources like OPC UA via SAP Plant Connectivity (PCo). Please have a look at the following SCN links that describe in detail how to do this:
http://scn.sap.com/docs/DOC-27223 (Learn the Basics)
http://scn.sap.com/docs/DOC-27545 (Quick Start)
http://scn.sap.com/docs/DOC-27546 (Sample Query for Data Acess)
Best regards, Hans-Jürgen