Erica Grieder discusses Mormonism and theology:

Richard J. Mouw of the Fuller Theological Seminary says that the key issue is Mormons say that God and man are part of the same species, apparently a reference to the Mormon belief that God has a body (“He has a body that looks like ours, but God’s body is immortal, perfected, and has a glory that words can’t describe,” as the Mormon FAQ puts it.) That’s theologically provocative, but given that mainstream Christians hold that Jesus is both human and divine, it’s not hard to see how the question might arise [bold mine-DL]. Similarly, some theologians object to the Mormon conception of the trinity as three distinct entities, as opposed to the mainstream view that sees the trinity as (as this LDS site puts it) “united in substance and in person in a way that is incomprehensible by man.” Again: theologically provocative, not dispositive.

As far as theological definitions are concerned, the teaching of the hypostatic union of two natures concerns something radically different from the “provocative” claim Grieder mentions: the union presupposes the uncreated nature of the divinity being united to human nature. While there were disputes about the created or uncreated nature of the Son, even Anomoeans acknowledged that the Father was uncreated and immaterial along with all of the other attributes of divinity. I suppose it is “provocative” to teach a modern form of anthropomorphism and to hold that God is material rather than immaterial, and it is also radically different from the theology of virtually all professing Christians since the beginning. It is so radically different that Islamic theology is closer to Christian orthodoxy on this question than is Mormonism, so, yes, it’s “provocative.” It’s also what orthodox Christians would identify as false. Understanding the Trinity as “three distinct entities” has precedent in the history of doctrine. This was a tritheist teaching that Christians of all the ancient post-Nicene confessions flatly rejected as the antithesis of Trinitarian doctrine.

If one takes the Nicene Creed as the statement of what defines the core of Christian doctrine, as the main Christian confessions do, tritheists believe in something profoundly different and incompatible with Christian teaching. There seems to be no point in dismissing radical differences in the two teachings. When adherents of both know it isn’t the case, it doesn’t show any respect for either of them to pretend that they are just slightly different versions of the same thing.