I'm wondering how the guilds work in terms of who can or cannot make a movie. I know that a major studio cannot release a non-union film, but I'm wondering if, for example, someone can legally have more than one job on a film. For instance, could a director also be the DP in a union shoot? I was told you can't legally do this... seemed a bit silly to me.

But I digress. What are some of the limitations set forth by the guilds regarding these things?

I don’t know the actual rules but I know that for years Robert Rodriguez wrote, directed, edited and was the visual effects supervisor (among other things) for his movies. During this time he was part of the writer and the director’s guild. He only recently dropped out because of their idiotic rules and regulations. So I believe you can do all of those jobs but I’m not sure to what extent.