Just taking a guess, "Not Our Hitler?"
Its just a weird ass change, especially for a name. I mean, calling him Hitler in the story makes more sense than Notler.
Hell, in all honesty, Alois Hitler was born Alois Schicklgruber - it is not that far of a stretch just to have him shorten his name to Gruber, therefore his son will be Adolph Gruber or something like that. And it makes more sense if you want a different Hitler.