Now I don't know the ins and out's of hognose care but it seems that a rodent diet, while controllable, may lead a little easier to obesity then the more lean amphibian diet.
Obviously this can be limited by feeding mostly lean, healthy mice, and not old retired jumbo breeders. Avoiding obesity can also be done with size of prey and frequency of feedings. I'm sure you can also get an obese hognose on an amphibian diet.
So, the connection I offer is not one of diet, but that of obesity. Fatty liver IS connected to obesity, without question. Not all animals that are obese will die of fatty liver disease, nor are all fld cases originally obese, BUT, obese snakes are at a much higher risk of developing fatty liver disease, either as a primary illness, or secondary to something else.
This info might lead someone to make the loose connection of;
mice-->obesity-->fatty liver.... where soon obesity drops from whatelse... laziness 
mice -->fatty liver.
I hope this sheds some light from my point of view 
Ian