And you're wrong again on Yellowstone being the only reason there are wolves in Montana and Idaho. If you look at the maps I linked to from Defenders of Wildlife you can see that the range of wolves extends from Canada through much of western Montana and northern Idaho, and a corner of Wyoming. The reintroduction of wolves in those areas involved much more than just the Yellowstone reintroduction.  The Endangered Species Act, which in the 1970's gave the wolves the protection they needed in Montana to re-establish  populations. There were 48 wolves in Montana's Glacier National Park a year before the human re-introduction of wolves into Yellowstone. Human engineered re-introductions also occurred during this time in central Idaho.

Although wolf packs were eliminated from Montana by the 1930s, tracks, scats, and/or observations of large canid-like animals were either reported or killed up until the 1970s. Most are thought to have been dispersers from Canada and little to no successful breeding activity was evidenced or sustained consistently through time.

In 1980, the Northern Rocky Mountain Wolf Recovery Team completed a plan which would guide wolf recovery efforts for a future wolf population in the northern Rockies of Montana, Idaho, and Wyoming. The recovery plan was revised in 1987. The plan designated three recovery areas - Northwestern Montana, Central Idaho, and the Greater Yellowstone - each of which included some portion of Montana.

Wolves from Canada began to colonize the Glacier National Park area in 1979, and the first wolf den in the western U.S. in over 50 years was documented there in 1986. The wolf population in northwest Montana grew as a result of natural reproduction and dispersal. By the end of 1994, there were about 48 wolves in and around Glacier National Park.

In 1995, three family groups (a total of 14 wolves) were captured near Alberta's Jasper National Park, transported to Yellowstone National Park, and placed in acclimation pens. They were held for 10 weeks prior to release. Two of the females subsequently denned and produced nine pups in Montana. Most settled in the same vicinity of their acclimation pens, demonstrating the potental advantages of a "soft" release technique.

Also in the winter of 1995, 15 wolves were reintroduced into the wilderness areas of central Idaho. These animals moved widely throughout central Idaho and beyond. Many of these wolves moved north, some to the upper Bitterroot Valley. In 1996, three packs produced 11 pups.

In the winter of 1996, 17 wolves were captured near Fort St. Johns, British Columbia, Canada and were again released into acclimation pens in Yellowstone National Park through a "soft" release. Twenty wolves were released in central Idaho as a "hard" release.

Wolf populations in Yellowstone National Park and central Idaho grew rapidly and soon became a source for dispersers to Montana. New packs formed outside the earliest core wolf areas and overall wolf distribution expanded. Wolf dispersal has been documented between and among all three federal recovery areas and the states comprising the northern Rockies. By the end of 2002, the northern Rockies wolf population met the biological recovery criteria of at least 30 breeding pairs in the northern Rockies for three years in a row. By the end of 2004, there was an estimated 835 wolves and 66 breeding pairs in the tri-state area. In Montana, there were about 153 wolves in 15 breeding pairs.

and from the same link:

Many people were also concerned about big game populations and hunting opportunity as a result of wolf recovery. Wolves do have the potential to impact populations of deer, elk, and moose. How much of an impact varies in space and through time and most importantly, it varies with other environmental factors such as drought, severe winter, overall carnivore density, or general habitat conditions.

Research in Montana and elsewhere has shown that predation in general may influence deer, elk and moose populations through changes in survival of young, death of adult animals, or a combination of both. Wolf recovery probably will affect hunter opportunity in some areas and not in others. As for other populations whose numbers fluctuate, there is no clear answer except that wolves will add another factor to consider among all the environmental and social factors wildlife biologists wrestle with every year when setting big game regulations. Hunting opportunities are then adjusted in response to all factors combined.