The designer that ships with the windows workflow foundation is quite tightly tied to the runtime. It's also not built using DSL Tools.
You can use DSL Tools to build workflow like designers which can put to any purpose, and are not tied to the WF runtime.
For example, if you wanted to build a workflow designer for business process modeling, or say to model scenarios when doing requirements capture, then you'd use DSL Tools to create it. You might then translate those models into a form that could be consumed
by WF, for those aspects of the business workflows that you wanted to automate.