We currently have a tag for cycles-render-engine , eevee-render-engine and blender-internal-render-engine but not an active tag for workbench-render-engine
I created the tag on an edit to a question recently when I noticed this, but it seems that the system has deleted the tag as an orphan.
As of this writing, we have roughly 24 questions referring to Workbench, so while it may not be the most popular engine, it may help organization in the long run.
Thoughts?