A little hair loss on the elbows on a rottie are pretty normal from the way they lay. The tiny scabs and sores can be from itching due to fleas, mites, dry skin, allergies or even a skin dermatitis to name a few.
First thing is to definitely rule out fleas. If your dog is on advantage or frontline, you can skip this step. If they are not, you should at least explore the possibility of fleas by examining your dog's skin especially around the rump area under a bright light. Fleas are fast and are a reddish brown color so you have to look closely. Frequently you will only see flea dirt (feces). If you find fleas dirt or what you think is flea dirt, get a moist white paper towel and rub it on the area. If it turns reddish color then it most likely your dog has fleas. A flea comb or lice comb run through the area may capture a live flea as well.
If fleas are ruled out, it may be dry skin. If you believe this may be the cause, I think your best bet would be to supplement your dog's diet with Omega n3 fatty acids. You can do this using fish oil capsules. You can read about fatty acids here:
Then there might be a skin condition such as staph dermatitis or yeast dermatitis. These skin conditions are generally seen with allergies. Staph usually occurs on the lower regions of your pet and tends to have small pimple type bumps. Shampoo containing Chlorhexiderm and/or Oatmeal can help with this condition. Yeast typically shows as a greasy area that has a sweet musty odor. Sometimes the skin can become inflamed, darker and thickened due to itching. Yeast likes areas such as between toes, armpits and ears. Selsun Blue Shampoo can help with Yeast dermatitis. When shampooing, lather and leave on 15 minutes before rinsing. These shampoos are not meant to be a cure, just a relief until your pet can see a Vet. Benadryl can be given to your dog, the dose is up to 2mg per pound every 8 hours for itching due to allergies.
You can read about allergies here: http://www.nhahonline.vetsuite.com/Templates/ContentPages/Articles/ViewArticleContent.aspx?Id=864
There are two types of mange and mange is actually caused by mites. Usually hair loss starts in specific areas of the body before spreading to other areas. Your vet can do a skin scraping to rule out mites.
Here is a site that goes over itching in dogs.
Hope these suggestions help.