Despite your link, there is no evidence by word or deed that Hitler was a Christian.
"My feelings as a Christian points me to my Lord and Savior as a fighter. It points me to the man who once in loneliness, surrounded by a few followers, recognized these Jews for what they were and summoned men to fight against them and who, God’s truth! was greatest not as a sufferer but as a fighter. In boundless love as a Christian and as a man I read through the passage which tells us how the Lord at last rose in His might and seized the scourge to drive out of the Temple the brood of vipers and adders. How terrific was His fight for the world against the Jewish poison. To-day, after two thousand years, with deepest emotion I recognize more profoundly than ever before the fact that it was for this that He had to shed His blood upon the Cross. As a Christian I have no duty to allow my self to be cheated, but I have the duty to be a fighter for truth and justice… And if there is anything which could demonstrate that we are acting rightly it is the distress that daily grows . For as a Christian I have also a duty to my own people." –Adolf Hitler, in a speech on 12 April 1922 (Norman H. Baynes, ed. The Speeches of Adolf Hitler, April 1922-August 1939, Vol. 1 of 2, pp. 19-20, Oxford University Press, 1942)
No matter how you try to spin this but clearly he proclaim he is christianity and doing God's work.
If he did sincerely repent and ask to be saved, then yes, God would forgive him. However, there is no evidence that he did that. He didn't leave behind a written note to that effect. Also, if he had truly repented, it is likely that he would not have taken the coward's way out by suicide. He would have stuck around to face judgment, publicly confess his sins, and proclaim to the world that persecuting and killing Jews was wrong. God could have greatly used him to destroy the enemies of the Jews. But it doesn't appear that Hitler made that decision.
"Around 1937, when Hitler heard that at the instigation of the party and the SS vast numbers of his followers had left the church because it was obstinately opposing his plans, he nevertheless ordered his chief associates, above all Goering and Gobbels, to remain members of the church. He too would remain a member of the Catholic Church, he said, although he had no real attachment to it.
And in fact he remained in the church until his suicide." (Inside the Third Reich by Albert Speer page 95-96)
Again , He took his life in church which he must had ask God for forgiveness before he commit suicide.
The same that we don't know what Hitler decided in his final moments, we don't know about Mother Teresa or Gandhi.
Gandhi said he was unconvinced by christianity and do not agree with their teaching.
You can find his answer to why he doesn't become christian. obviously he doesn't believe in God/Jesus or in heaven.
source:
Ask Gandhi
Luther was just a man, and his writings were not inspired Scripture. If he was seeking revenge against the Jews, he was doing that in his own heart, not God's.
Funny thing is today we have church filled with christians honor his name. Lutherian Church !!