I don't understand the difference. At least as long as it involves web. There should be no divide between the two. A separation between designer and developer is at best moot, at worst a hindrance against getting where you should be in the process. In general, collaborations between the persons involved in a development process should be simple enough: give everyone access to a source-control system, and let them play with the code themselves. Assign tasks, and let them commit changes. Git, Subversion or similar.