The official positions of at least several major denominations do indeed hold that the theology of Latter Day Saints is not Christian:
practices of the Church the Mormons are not to be considered as belonging to an "ecclesial community not in full communion with the Catholic Church" [...] if a Mormon wishes to become Catholic, the norms that ...
In recent years, there is more acceptance to acknowledge LDS as christian, despite the fact that certain parts of the doctrine are different and the baptism is not accepted as valid.
In 2008, there was an ecumenical conference where they were invited among their fellow christian ministers:
Christian Apologist Sean McDowell has published an article on his website where he analyzes and raises some objections to Joseph Smith's martyrdom. Below a few quotes from the article:
WAS JOSEPH SMITH A MARTYR?
In my recent book The Fate of the Apostles, I make the historical case that the apostles were all willing to suffer and die for ...