We use Composer here but we do not have an EPDM system in place. Composer will create smg. formatted files. If you are working on a composer file and want to import some solidworks files into your composer doc it will not let you if someone has the solidworks file open you are trying to import. That includes changes/updates to the composer smg file using the solidworks file if it is open.
We use both. InDesign I have set up with a simple 2 state workflow (no rev). Composer I have moved away from revs on it. Instead I link the images into a word document to create a PDF. I handle the revs through the the office doc workflow.