Yes your dog can benefit from DERMA-IONX. Demodectic mange is an opportunistic infection because the immune system is weak. I would use the homeopathic DERMA-IONX both internally and externally to heal and soothe the skin as well as rebuilding the immune system. Giving probiotics, vitamin C, MSM, and Omega 3,6,9 will all help in that goal, too. (Vetionx carries PROBIOTICS and OMEGA 3,6,9. The C and MSM you should be able to find at a health food store). DERMA-IONX also helps the body to better utilize the supplements for faster results.
I would start with a 1/2 dose of DERMA-IONX twice a day. It is easiest to add it to the food. I would offer filtered drinking water to avoid chlorine or fluoride.
Diet is important. I am glad you are feeding grain free. According to Chinese food therapy I would offer a cooling diet especially during the summer and because the skin is warm. The protein sources that are considered to be more cooling are fish and turkey. I would stop the chicken for a while and switch to turkey if your dog is not allergic to it.
I would bathe with DEFENDEX shampoo when you need to give a bath since it is soothing and nontoxic. The shampoo is very concentrated so just use a small amount.
Please let us know how you progress or if you have any other questions.