Hi Allyson,
Maybe repeat the ACTH stim test to confirm Guelph's findings. Impaired wound healing, increased abdominal fat deposition, and a rounded abdomen in general are all consistent with the diagnosis, of course, and I know you're aware of that. So I get that there's something about the dog that doesn't ring true with Cushings, but the only way to be sure now is to repeat the test when the dog is considerably less stressed.
I had a case like this early in my career. I ended up having to get a surgical silk mesh from the local hospital to put over the linea alba, so that it would finally heal properly. So this kind of problem is common in humans and is not always tied to Cushings.
Up until that point in your story, the liver enzymes, irritability, and adbomdinal distention were all consistent with Liver Blood deficiency, and potentially treatable with Xiao Yao San. XYS addresses atypical Cushings so may form a link between what Guelph and you are seeing. Blood deficiency isn't necessarily associated with a huge abdominal fat supply, but is associated with impaired wound healing and neck pain (wind invasion secondary to Blood deficiency; spasm). So it's the other diagnosis I'd entertain. The pulse and tongue will hopefully clarify which you're dealing with, as well as the response of the pulse to various acupuncture points.
I hope that helps you out a little.
All the best,
Steve