I agree with several of the points already made here by Gaz and Grant. The culture starts at the top, if upper management fosters a collaborative environment, then each side can recognize the contributions of the other and everyone feels recognized. Some developers know a lot more about the DBA side of things than DBAs credit them for and vice versa. But too many on both sides like to maintain the walls of their respective kingdom, like there are big secrets to protect. Ultimately working together is what will drive the organization forward most efficiently.