My Dog Has A Sore On His Tail?

My corgi mutt is allergic to everything. We keep him, my other dog, and our cat on flea treatment all the time. We don’t have carpet. He has had his issues with itching his fur off, hot spots, etc, and has been in to see multiple vets. For a couple years we were making raw food [bison or lamb with fruits and veggies over beans and rice, beef and chicken are big no-nos] but recently we tried to get him back onto single protein dry food. We have tried venison, and currently he is on wellness whitefish. Currently he looks like a hairless raccoon, so obviously it is time to switch him back to the raw food.
A few days ago, I noticed him chewing his tail, on the top near the middle [its curly] his fur is dense there, but it started getting crusty from some scab he was licking at all the time. Today it looked like it was spreading, so I shaved the area to get a better look. It is swollen in a few areas.and some places it looks like a loose scab, and in other places it is just raised and irritated, and mostly its dry, but one one side it looks moist, but it isn’t like.. open and seeping. Does that make sense? I don’t see any abrasions, like a wound or bite that could have gotten infected….
I put some antibiotic ointment on it, and bandaged it up, but I am worried if the wont is moist, that maybe this wont be the most effective thing. If it is allergies, then switching his food will take care of it, does it sound like it could possibly be anything else? I wouldn’t be asking, but this is already unlike any of the “normal” abnormalities I have seen in this dog thus far.
My poor itchy pig