I do not know what the general Trump supporter population heard, but I know one person who was well aware of the Hitler comparison (they kept bringing it up). To them, Hitler was a horrible person who killed millions of people, so the comparison to Trump was absurd.
These people have been fed a steady diet of fear, anger, and hatred, all wrapped in the belief that Trump is being victimized by everyone. For those who believe what Hitler did, it probably came across as hysterical fear-mongering.