"No, it's true, I swear! The coffee machines on our side can do both espresso and latte! And all the American barracks have 2-ply toilet paper! It used to be only 1-ply, but then last mo— What do you mean 'this guy is useless', I've just given you everything!"

Probably not so much state secretes but he can provide inside on how the US military trains soldiers, command infrastructure, and probably has some relevant information on how the border is guarded.

But mostly he would just be used for propaganda. "Look how bad the outside world is, people are running here for a better life".