Dashboard is aimed for monitoring and tracking, so it's less likely to be used for editing purpose. But do you mind sharing your use case of why you want editing in Dashboard?
Though the built-in tools do not provide editing function, there is a custom addin for dashboard that you can use (available at http://www.arcgis.com/home/item.html?id=8f2d5c5632254c57b355f0296632b813). The editor tool can be used to draw polygon features on the map widget (it works with polygon layer only since the tool was created for a specific user scenario). Please let me know if that helps.