It certainly helps for the project’s communities to have good social engineering skills. From tactfulness, to humour, to controlling one’s temper, to saying “Thanks” and congratulating people for their contribution, to timely applying patches and fixing bugs - all of these makes contributing to a project and using the program more fun and less frustrating.
Often, social engineering should be made part of the design of the software, or the web-sites dedicated to it. For example, it took me several iterations of having to fill the same project form in the GNU Savannah software-hub, only for it to be rejected, and me having to follow the process again. Despite the fact the admins were polite, it still was annoying.
Eventually, they implemented a way to save previous project submissions and to re-send them, so future users won’t become as frustrated as I did.
Again, some projects have succeeded despite the fact they had, or even still have, bad social engineering. But adopting a good software engineering policy can certainly help a lot.