In the NBA, as you say, the forearm is legal as long it's not used to force the dribbler away from his path. In high school and men's NCAA, the forearm is technically a foul, although many officials will try to warn the defender to remove his arm ("Hands off!!") before actually calling a foul.
In 1-on-1 driveway basketball, I'd say it's perfectly legal
Most driveways have their own "ground rules" anyway. My favorite ground rule was at a friend's house and his mom had lovely flowers lining one side of the driveway. If the ball hit the flowerbed, the ground rule was everybody run home! We would sprint and go through all kinds of contortions to keep the ball from bouncing into the flowers. Good times.
