DevForce EF is built "on top" of ADO.NET EF. The limitation of 1 EDMX = 1 database still holds. In DevForce, though, you can include multiple entity data models in a single DevForce "domain" model, as is shown in several of the tutorials.
On the latter part of your question about shifting to a different database - I assume you mean having a single CSDL (conceptual model) with different SSDL (storage model) definitions? That is doable, and one of the reasons why the EDMX at runtime actually consists of 3 separate resources (conceptual, storage and mapping). DevForce doesn't do anything to help or hinder this support, and I'd recommend the ADO.NET EF forum (
http://forums.microsoft.com/MSDN/ShowForum.aspx?ForumID=533&SiteID=1) or other MS resources for help on the mechanics of separating the models.