Good for him. The nice thing about having property rights is that when you own property you get to do with it whatever you like. If you have a passion for an issue, you can use that passion to make more money and then put that money to work solving the problem. That's the whole vision of free markets and individual liberty.
I'd be singing a different tune if Depp was insisting that the government buy the property and give it to the Indians. But if he wants to do it, more power to him.