The Christianity issue aside, Mittens is very likely a nominal Mormon.
There’s nothing so convincing as an “I don’t care, but ...”
Having said that, I am withholding judgement on whether Mormonism is a cult or not.
To me, though, a person's religious philosophy is one of several criteria that I would impose when considering whether to support a candidacy or not.
In Romney's case, the fact that he is a Mormon does give me some pause, whereas being a mainstream Christian would not. Not as much pause as a Muslim or collective authoritarian might give me, though.
Also, the Mormon issue wouldn't be a litmus test for me with respect to Romney. There are several other, more cogent issues which utterly disqualify Romney, to my thinking.
The Second Amendment and RomneyCare immediately come to mind, for instance.