Greg, I don't know the actual extent of the cold hardiness of Dancy Tangerine. but it is probably pretty much the same of most mandarins. The book "The Citrus Industry" says about Dancy: -- " The Dancy is to be commended because of it vigorous, strong growth, its cold-resistant quality, its abundant and regular fruiting habits, and it highly attractive, excellent quality fruit. Moreover, it is resistant to disease...."
I used to have a Dancy Tangerine, and it was an easy, and trouble free tree to grow, The main problems with Dancy are the small size of the fruit and its too numerous seeds. Because of the small size of the fruit, I finally just got rid of it. Good luck. - Millet (688-)