Has anyone managed to record video using Nvidia's ShAdowplay application?

Yes, it works just fine.  You just need to set it up properly.

 

After you select ShadowPlay (from GeForce Experience), click on the toggle switch (puts the recorder on standby). Then click on the Preferences icon (the gear icon under the toggle).

Under the monitor, check "Allow Desktop Capture." And you should be good to go.

Thanks Arwen