If it's a red patch, whatever caused it in the first place he now doubtless has a bacterial infection (maybe cause by the scratching). He should get to the doctor and at least get a series of antibiotics. The doc can do testing for various things (yeast infection, fungal infection, bacterial infection, STDs, etc.) I wouldn't put this off -- when I got cellulitis on my arm it was a VERY stubborn infection and took two rounds of antibiotics to knock down, and that was just out in the air on my arm, where there is no moisture or source of bacteria. Take it seriously, drag him to the doc if you have to
Your husband may get a fungal infection called jock itch. Fugacil cream can help eliminate the fungus, clear the rash and relieve the itch. To be sure, you should ask him to get tested by a doctor. Rash on the scrotum can be caused by a number of factors, including jock itch, chafing, intertrigo, contact dermatitis, crabs or pubic lice and even an STD.
The application of coconut oil will give your husband relief. This oil has been known for soothing the rash and blocking moisture.