Oh, poor Snickers! I am just seeing this thread.
An overgrowth of Clostridium is a suspected cause of HGE. Lady had HGE three times in four months a couple of years ago. Very scary.
Hemorrhagic Gastroenteritis (HGE)
In Lady's case, a homecooked diet and adding probiotics was the solution. She never had HGE again. I think having a nutritionist develop a diet for Snickers is a fantastic idea.
I am glad you took him back to U of T. He is in excellent hands. Diagnosing dogs with multiple health issues can be tricky.