I plan to use Blender exclusively as a video editor. I have put together a video in the sequencer and it renders without issues. However, I have also crated a node group to do some sharpening. It seems to be working fine in the viewer node, but is not reflected in the file output node, the sequence editor window or on the rendered video.
To bring the result of your nodes to the VSE you need to have an Output->Composite Node at the end of your node chain. On the VSE add a scene strip (Add Scene->Scene) and disable Open GL Preview.
If you just want to render the events in the compositor as a file to later rework on the VSE then you need to disable the sequencer temporarily. Then your file output nodes will work as expected.