Local knowledge is always useful. Numerous times throughout history people have gone into a new situation interacting with the locals, without understanding what was happening. Reading an article in New Scientist, which mentioned that psychologists from the west going to help in the Boxing Day Tsunami faced unexpected problems. They didn't understand the trauma of people different from them. They faced symptoms they'd never heard of, which didn't fit into western psychology. Therefore they found it hard to treat them.
Similarly, people going to try and help people need to make sure that they listen to the locals. They probably know alot more about their situation than you do. Most importantly, if you don't have the support of the people you are trying to help, what you're doing is probably pointless.