Braking practise?

I am not familiar with american (and chineese and russian) braking practise.
In Europe brakes to UIC norms can be gradualy reeleased but as far I know in USA, China and Russia the brakes are completly released immidiately when air is charged into the brake pipe.
When going downhill with locos equiped with dynamic brakes, are the air brakes applyed to some degree and the speed regulated by the dynamic brakes?

It depends on the severity of the grade and the weight of the train as to whether the engineer needs the air to assist in the dynamic process.

Also with gradulated release, North American locomotives, most of them, are set up for freight and passenger air systems.

As you know, freight cars can't be gradually released, it has to be a full release. Passenger cars can. So in the event you have a freight locomotive pulling a passenger train, that engine has to be set up for passenger service.