This is not only how it is (was) rendered in German: because of the phrase's notoriety, it is left untranslated in English. Whether in Nazi movies or among modern neo-Nazis, the German phrase is always used -- never "Hail Hitler" or "Long live Hitler" or any such translated form. "Hail Caesar!" yes, but always "Heil Hitler!".

Regarding Harry's comment: "Heil" here is not functioning as the imperative of "heilen" but rather as "das Heil" = salvation. Thus "Hitler" is in the implied dative and to say "Heil Hitler!" means literally "salvation to Hitler!"