This question cannot be answered logically. Hitler hated America, Arabs, Muslims, Jews, etc. While the terrorists do not represent Islam, Hitler's simple mind would have probably thought so. While the attack was done upon one of his enemies (America), it was performed by people who are of Arab ethnicity and claim to follow the religion of Islam. I don't think he would have cared.
It Hitler was in charge, we'd have had NO 9/11. Jewish multiculturalism and their shenanigans in the Middle East caused it.
Arabs killing white people ? He would not be happy. But maybe since USA was his opponent during WW2, he would be happy.
He probably would only care about Jewish People and other people that he desgracied to get killed in those attakcks
Hitler would have been appalled that white, blue eyed people were killed.
"There better have been the Jewish in the twin towers!"
It's a very sad day,lost 1's rest in Peace!