for one, you aren't the judge of that, god is, you have no idea if he repented or not, his relationship with god etc. You aren't the gate keeper for heaven nor are you suppose to even judge others.
it is the no true scotsman fallacy, just like the people that say suicide bombers aren't true muslims, it's all nonsense, the book is up for interpretation. You already said the only unforgivable sin is rejecting god, so how in the same breath can you say Hitler is not in heaven? he clearly accepted christ, his other sins can all be forgiven.
Ok, there's a number of things I need to address in your post so my response will be longer than your post.
You are correct in that I am not the ultimate judge of whether or not someone ended their life as a Christian or not. Ultimate judgment rests with God...he knows the reality. I also don't have certainty there wasn't a deathbed conversion of some sort. What I do know is the record of works these folks left in their lives does not jive with Christ in anyway whatsoever.
"nor are you suppose to even judge others" - this is a very common misunderstanding of scripture. Many folks have "pocket verses" they memorize....both believers and nonbelievers alike. Common spins on verses I see repeated are "do not judge others...." and "money is the root of evil". Both cited verses are incorrect and incomplete, but we'll stick with the concept of judgment here.
Now, as is common, the verse in Matthew 7 is often split in half and pulled from surrounding context. Here is full passage with the verse commonly cited in red:
Matthew 7:1-6
1 “Do not judge others, and you will not be judged.
2 For you will be treated as you treat others. The standard you use in judging is the standard by which you will be judged.
3 “And why worry about a speck in your friend’s eye when you have a log in your own?
4 How can you think of saying to your friend, ‘Let me help you get rid of that speck in your eye,’ when you can’t see past the log in your own eye?
5 Hypocrite! First get rid of the log in your own eye; then you will see well enough to deal with the speck in your friend’s eye.
6 “Don’t waste what is holy on people who are unholy. Don’t throw your pearls to pigs! They will trample the pearls, then turn and attack you.The vast majority only quote "do not judge others" and stop.....that's it....."Do not judge others! It's in the bible and here you are a Christian passing judgment!"
The idea in the passage is how to appropriately judge others or hold them accountable for their actions.
I'll illustrate with a simple example: don't come to an alcoholic and judge them for their drinking while you're polishing off a bottle of Jack Daniels in front of them. It sets a bad standard LOL.
As believers we are called to hold our fellow believers accountable for their actions. There are standards we are to adhere to and the foundation of those standards is Christ. We are absolutely meant to judge each other, but we do so according to God's standards and not our own. Hitler has claimed affiliation with Christianity yet compiled an almost unprecedented record of murder, torture and evil.....I absolutely judge his works according to God's laws and his "Christian record" falls completely short.
Why we debate this I'm not really sure?
Now, I never once said the unforgivable sin is rejecting God. I did say we have to make a choice to accept or reject God. I also stated that God does not forgive all people. Those that willfully reject Christ (and go to their death in doing so) will not have their sins forgiven.
We clearly know that the notion of rejecting God as the unforgivable sin is false because many have rejected God at some point in their lives and later come to God fully embracing him and desiring a relationship with him. This is the root of true conversion from unbelief to belief and the power of Christ's saving grace.
The unforgivable sin noted in scripture, by Christ, was attributing the works of Holy Spirit to the demonic realm of Satan. After Christ publically healed a demoniac the Pharisees claimed his ability to exorcise the demons was fueled by demons. Christ knew their thoughts and stated the following:
Matthew 12:31-32
31 “So I tell you, every sin and blasphemy can be forgiven—except blasphemy against the Holy Spirit, which will never be forgiven. 32 Anyone who speaks against the Son of Man can be forgiven, but anyone who speaks against the Holy Spirit will never be forgiven, either in this world or in the world to come.Again, the larger context of the passage is to not attribute the things of Holy Spirit to the things of Satan and his demons.....BIG "no no"!
How is it clear that Hitler accepted Christ? Because he said he related to Christians or attended church LOL?!
Evil, twisted men claim all sorts of things in one breath and then violate those same things in another. Hitler apparently claimed Christ in the midst of the murder of millions...that behavior didn't cease nor does it align with Christ. The only certainty we do have about Hitler is that he was a very articulate, intelligent, sick, twisted, evil man.
Accepting Christ isn't about a magical spell....quoting words in certain order accomplishes nothing. God knows the contents of our hearts and can easily discern the fakes from the genuine article. Scripture addresses this topic in a number of places......our works vet our claim of faith in Christ.
Again, as I noted yesterday:
James 2:14-26
14 What good is it, dear brothers and sisters, if you say you have faith but don’t show it by your actions? Can that kind of faith save anyone? 15 Suppose you see a brother or sister who has no food or clothing, 16 and you say, “Good-bye and have a good day; stay warm and eat well”—but then you don’t give that person any food or clothing. What good does that do?
17 So you see, faith by itself isn’t enough. Unless it produces good deeds, it is dead and useless.
18 Now someone may argue, “Some people have faith; others have good deeds.” But I say, “How can you show me your faith if you don’t have good deeds? I will show you my faith by my good deeds.”
19 You say you have faith, for you believe that there is one God. Good for you! Even the demons believe this, and they tremble in terror. 20 How foolish! Can’t you see that faith without good deeds is useless?
21 Don’t you remember that our ancestor Abraham was shown to be right with God by his actions when he offered his son Isaac on the altar? 22 You see, his faith and his actions worked together. His actions made his faith complete. 23 And so it happened just as the Scriptures say: “Abraham believed God, and God counted him as righteous because of his faith.” He was even called the friend of God. 24 So you see, we are shown to be right with God by what we do, not by faith alone.
25 Rahab the prostitute is another example. She was shown to be right with God by her actions when she hid those messengers and sent them safely away by a different road. 26 Just as the body is dead without breath, so also faith is dead without good works. 
