Yeah I don't think Attila would ever be declared emperor, even if he is converted to Roman Christianity or is at least pro-Christian. However, I don't think that means he would be completely separate from Roman politics. He may not be declared Emperor or Governor or anything like that, but with a large army and a position more advantageous to the Roman style of Christianity he would definitely play a role in Roman politics.
Something that could be interesting would be how this would affect Arian Christianity, especially if Attila is actually converted to Roman Christianity. Arianism was most popular in Germania during this time period, and with a Roman Christian empire in northern Europe, could it have spread to the north earlier, thus putting a stop or at least a hindrance to the power of Arian Christianity in Germania? Could this mean that the Germanic Barbarians are less inclined to invade Rome, especially with a more pro-Rome Attila? Such a timeline could mean a later collapse of the western roman empire, and under different circumstances.