OutdoorLife article on tracking deer with dogs
New York, Wisconsin, Maine, Vermont, Indiana, Texas, British Columbia, Kentucky, Michigan, Ohio and Alaska all recently passed laws to allow the use of dogs to recover deer and other big game. It is also legal to use a dog to track wounded deer in most of the South, though some states regulate it on the county level. In general, the practice is gaining acceptance across the country, but you should review the regulations to be sure it's legal where you hunt.