Very simply, if this problem even arises, you probably ought to leave.
For one thing, the notion of having a single "project director" who runs both the marketing and engineering sides of the project is stupid. Instead, what you want is a product manager who is in charge of the marketing side, and a separate project manager who is in charge of the technical side. These two need to respect each other and work together adequately. If they don't, there will be trouble.
Also, you shouldn't have to deal with a marketing department full of assholes. If marketing and engineering don't get along, the product is in trouble. It really isn't true that all marketers are assholes; just most of them.
One thing I really like about my current company is that it has a severe shortage of assholes. I like all the engineers and their managers, I like all the marketing people, the HR people, the MIS people, the receptionist, etc. They're all competent at what they do, and pleasant people as well. I think the fundamental reason for the company being this way is that its founders were very nice, highly competent people, and they did a really good job of hiring people who shared those qualities. So, from this, I infer that a company full of assholes was probably founded by assholes, or at least, by people who weren't very good at filtering out assholes from their candidate pool. Or perhaps the company has just been around so long that the few assholes who did manage to get in have had time to spread their condition throughout the company. Whatever the reason, a company with a lot of assholes, even if they're all confined to the marketing department, is just not going to be a great place to work.