Hitler's generally agreed birth time is recorded as 6:30 pm, which gives an Ascendant of 26 degrees 41 mins of Libra. A quoted time of 6:30 tends to indicate (to me, at least) some rounding - more an estimate than an exact timing. It's rare that someone holds a stopwatch to time the exact moment of birth.
However, for Hitler to have a Scorpio Ascendant, he would have had to be born later than 18:49, nearly twenty minutes later and it would be very unlikely that even an estimate based on this time would be rounded down to 6:30. So I think that the Libra Ascendant holds.
Modern Astrology doesn't bother with the old subdivisions of a sign, such as the Terms or Bounds. Hitler's recorded birth time puts his Ascendant in the Bounds of Venus. However a birth time of 6:41 would shift it into the Bounds of Mars. It's just possible that might have been rounded down, however I still doubt it.