Taken from http://rawfed.com/myths/stomachcontents.html
Wolves do NOT eat the stomach contents of their prey. Only if the prey is small enough (like the size of a rabbit) will they eat the stomach contents, which just happen to get consumed along with the entire animal. Otherwise, wolves will shake out the stomach contents of their large herbivorous prey before sometimes eating the stomach wall. The following quotations are taken from L. David Mech's 2003 book Wolves: Behavior, Ecology, and Conservation. Mech (and the others who contributed to this book) is considered the world's leading wolf biologist, and this book is a compilation of 350 collective years of research, experiments, and careful field observations. These quotes are taken from chapter 4, The Wolf as a Carnivore.
"Wolves usually tear into the body cavity of large prey and...consume the larger internal organs, such as lungs, heart, and liver. The large rumen [, which is one of the main stomach chambers in large ruminant herbivores,]...is usually punctured during removal and its contents spilled. The vegetation in the intestinal tract is of no interest to the wolves, but the stomach lining and intestinal wall are consumed, and their contents further strewn about the kill site." (pg.123, emphasis added)
"To grow and maintain their own bodies, wolves need to ingest all the major parts of their herbivorous prey, except the plants in the digestive system." (pg.124, emphasis added).
This next quote can be found on the Hunting and Meals page at Kerwood Wildlife Education Center.
"The wolf's diet consists mostly of muscle meat and fatty tissue from various animals. Heart, lung, liver, and other internal organs are eaten. Bones are crushed to get at the marrow, and bone fragments are eaten as well. Even hair and skin are sometimes consumed. The only part consistently ignored is the stomach and its contents. Although some vegetable matter is taken separately, particularly berries, Canis lupus doesn't seem to digest them very well."
So this is taken from wolf experts.