The black dots are more than likely simply angiokeratomas. Basically, they arise from blood vessels in the area and may appear after injury or trauma to the area (if he got an injury or from being tightly compressed in his briefs). However, if you are very worried about these dots, you can be tested yourself just to get clarification that there are no sexually transmitted infections.
The itchy scrotum can be from pruritis or from "jock itch". If he has sweat in his gential region that stays in the area for hours at a time, it could cause a fungal infection called jock itch. Or else he could have a yeasty type infection in the area. The fungal infection could be treated by an over the counter cream like lotrimin or tinactin. A yeast infection could be treated by miconazole (the same thing you would use for a yeast infection).