CreatedorMade There is no thing called greenlight support. Greenlight has no features. On greenlight you only post a page and a video and people vote for it. No exported game is needed. And later IF you get greenlit you can publish your game.
So when you're greenlit you can export your game with node webkit and upload it on steam and it will work just fine right out of the box. But if you want to use achievements and other steam features you then need to use the greenworks plugin which aldready exist and now works thanks to MadSpy who have modified it to work with NW12.
And hopefully we'll soon have a plugin that works with the latest version of NW as well.
So MadSpy is one of the people on this forum who knows the most about steam integration and have helped many of us who have a game on steam.
Good luck with your project.