He adds his brother’s produce to his own so that the government can market it without (the government) knowing

Praise be to Allah.

It seems from your question that the state is only marketing the dates grown by the people who are taking part in these projects so as to encourage and help them, and it is not doing that for other people. Hence it is not permissible for you to take some of your brother’s produce and give it to the government unless you tell them about that, because this comes under the heading of deceit, lying and consuming people's wealth unlawfully, and all of that is haraam. 

What you should do is cooperate with the government in the beneficial things that it is doing, so that these efforts will be successful and will bear fruit, and this will prompt the government to do more beneficial things. 

As for tricking the government by doing such things, this is lying and deceit, and it may ultimately lead to the cancellation of these projects, so those who do these tricks will become the cause of hardship for the people. 

And Allah knows best.