If there really are ulcers, those are typically caused by bacteria in the stomach, like H. Pylori. What antibiotics were given, and have they helped at all? Clostridium infections can cause blood too - was a GI Panel, testing for things like clostridium ever done (it's a pretty expensive test). Probiotics are a must, as well as other gut support, like the slipperly elm mentioned, l-glutamine, etc.
Coat quality can be caused by a lot of things, from not absorbing ingredients, to having an unbalanced diet.
The only way to know for sure what is going on in the gut is with an endoscopy/colonscopy, which is pretty expensive, and has to be done by an internal medicine vet. If might be able to find one here by looking under the specialty SIAM: http://www.acvim.org/PetOwners/FindaSpecialist.aspx
My dog is allergic to potatoes and peas. She can't eat chicken or fish, and is on a no beef trial right now. I feed cooked lamb (Costco has the best price). You need to pick one protein, and one carb/fiber source. I haven't picked them up yet, but the vet wants me to try steamed turnips of all things. Green beans have worked well for my dogs that aren't allergic to peanuts. But all the dietary changes alone won't help if it's an infection or inflammatory bowel disease and medications are needed.