Hi
EP or NWBC which are browser based front end applications, works as presentation servers to access the features of dealer portal application. Your core dealer portal application will be in ERP only. To use dealer portal, you need to activate the business packages irrespective of front end applications. Check sap help portal for IS-A-DP for further details.
By assigning the standard roles, you can access dealer portal functionalities through desktop browser. Same URL, can be configured in NWBC and access it.
If you want to customize the presentation then enterprise portal is an option.
Thanks
Sasidhar Gupta