I had a professor in college who did a lot of research (paid research) with a golf ball company. Golf balls are dimpled as they primarily see form drag; their fat, round shape punches a hole in the air. That creates quite a wake (suction, eddies) behind the ball. If you can reduce the "suck" on the back, you can make it fly further. The dimples get the boundary layer turbulent and allow it to wrap a little further around the ball, reducing the form drag on the back.
Airplanes in particlular have more skin friction (and lift induced drag) than form (shape) drag. Dimpling an airplane would only hurt you. BUT, you do see a form of this, vortex generators, in key areas on airplanes, to help keep flow attached, particularly at high angles of attack.
Cars are somewhere in the middle. Probably more form drag than skin drag. But there is no free lunch here...companies invest millions (billions?) in R&D on cars to get the best fuel economy that they can. Thousands of hours of wind tunnel testing. Don't you think if it was a simple as throwing some dimples on there, they would have already done it? They would have I can assure you.
It could be interesting to try this on a short, fat rocket like a Minnie Mag. But, I dare say the boundary layer is already quite turbulent by the time it gets to the base of the rocket and dimples toward the bottom of the rocket would do very little to mix that layer up and help it stay attached further down the rocket. A boat tail would be more effective, but then your Minnie Mag wouldn't fly straight. Always compromises....
