I'll have a closer read as it looks quite involved.
I'm new with ignition so no, I'm not sure, but it does look like Siemens OPC-UA server (driver-interface whatever you call it) does not support structured data. I think what they're referring to is the pre-Version 4.4 when every tag had to be created and indirectly addressed in ignition designer; versus now with V4.4 I setup an "interface" containing the tags I want to access and in ignition I can just drag and drop them.
But if that way (old way) works for UDTs then I may go that route, I'll check it out.