We have a patch for DevForce 6.0.1 that fixes most of the problems when working with multiple entity models in the same solution. This patch will also let you enable/disable DevForce code generation on a per EDMX basis (toggle this on the properties page for the EDMX).
You can get the patch here:
[Edit: Link removed. This has been superceded by DevForce 6.0.3]
If you have an existing solution, you should right-click on each .tt file and select "Run Custom Tool" to get the new code generated.
Edited by ting - 09-Jun-2010 at 6:07pm