Do people have a right to control their history and what is written about them? I think not. I also don't think that the larger occupying or migrating group does either. It should all be written down and recorded by a third party that has no other interest other than to record history. The reason I believe this is because bias plays a huge factor when a people write their own history.
Take North Korea for example. Their history books portray a completely different story of their successes and their struggles. Now I know they aren't a small group indigenous people, but they are just a representation on the macro level and can be applied to much smaller groups as well. All you have to do is take a history book from England and one from the United States and compare the story of the American Revolution. You will find that the stories differ very greatly, but if you picked up a book from Thailand (The only Southeast Asian country to never be colonized) that is written about the American revolution, you might find an unbiased report.
Now when a scholar enters into a situation where he is recording the intricacies of a culture, he has the duty to not publish erroneous facts but on the same hand he must not be afraid to publish something that the people might dislike or find untrue. All knowledge about a culture is fair game, we must learn everything from a culture, big or small. There is one little exception, and that is if a certain piece of knowledge is potentially a big money maker.
One example of this code of ethics is displayed by Ethnobotanists. They study the relationship between man and plants. One of the largest employers of Ethnobotanists are pharmaceutical companies. They send them into remote villages in order to speak with tradtional doctors in orders to find plants that can contribute to modern medicine. In fact, when you go in the drugstore 1 out of every 4 drugs in there were derived from plants, and 89% of those were found by talking to a local folk doctor (Balick, 2005, p. 25). Is it fair to go into a village and learn of a drug that will make billions of dollars in the U.S. and then compensate them with nothing? Absolutely not. Is it fair to learn of this drug that could save millions of lives and not produce it because it is the knowledge of this indigenous tribe and they have sole rights to it? The answer to that is no as well. So a happy balance must be found where everyone can benefit from the knowledge and the original keepers of this knowledge are compensated. This example was not mentioned just for the topic of medicine, but for any type of knowledge or practices that a people utilize that can be applied to another culture.
It is the duty of the scholar to learn report everything he can about a culture, but when the knowledge will result in a large financial gain for another party, the curators of that said knowledge, technique, or invention, should be compensated appropriately for protecting and developing it through time. By using this rationale, it in now way interferes with free inquiry or academic freedom.
Balick, Michael J., and Paul Alan Cox. Plants, People and Culture. 2005.