All Wikipedia content is copyright the original authors under the terms of the GFDL. Anyone is free to re-use that content for any purpose, subject (in this context) only to two conditions: (1) proper attribution of the original source, and (2) the re-used content is also placed under the GFDL licence - i.e., the entire article is free for anyone anywhere to re-use for any purpose.
I have no idea what, if any, licence applies to Opus material sourced from elsewhere (including the material that you or I contribute). Maybe this is spelled out somewhere, but without knowing the terms of copyright and who owns the text and under what conditions, I wouldn't want to put any effort into contributing myself.
But unless Opus material is covered under the GFDL, using Wikipedia text would make a real mess of things.