Hitler still becomes Chancellor (it's kind of hard to not appoint the leader of the largest party in the Reichstag to the Chancellor's position), and World War II starts slightly later, as Hitler presumably needs Kaiser Wilhelm (who presumably is still Germany's head of state) to die first in order to seize dictatorial powers.
I don't think it would be necessary. Italy had a king and Japan had an emperor when they entered in the war.
Emperor Hirohito literally supported Japan's participation WWII, and the King in Italy was presumably a supporter of Mussolini.
I can't see Kaiser Wilhelm being willing to fight the major European Powers a second time.
