From what historical evidence we have of his last days--he committed suicide--, Hitler did not repent of his sins and trust in Christ as his Lord and Savior. In fact, he hated Christ and Christians along with Jews and others. So, if I had to make a judgment upon his current residence, I would conclude that he is separated from God and will one day end up in the Lake of Fire.
Yes, he was an evil person. However, all human beings are evil and spiritually depraved from birth. So we are all lost and on our way to hell. Only if God intervenes and saves us from our sin against Him will we avoid that destiny.