I sadly can not answer your entire question, I'm not equipped to fully examine how the average American would have viewed the Kaiser or Germany. But I did want to take a crack at it slightly if only because Atlantis is one of my favorite films. To start I would like to say Atlantis is actually set in 1914 and unless it takes place prior July 28th it is likely Milo is not looking to the future but the present.
American opinion of the war at the start was broadly neutral, there was some sympathy with Britain against Germany, but also a fair bit of anti-Tsarist sympathy with Germany against Russia^1. Though on the whole there was a slight bend against Germany because it was seen as the aggressor^2. This makes make a degree of sense if you were an outsider looking in as the Average American was. Broadly speaking the actual war (not including the events that precipitated it) started with three major German lead/caused events. Austria-Hungary's Invasion of Serbia with German support, German Declaration of War on Russia and France, and the German invasion of Belgium which was neutral thus bringing Britain into the war.
With that in mind, however, Milo is not the best use case for what the "Average American^TM" would think of the conflict. Milo is portrayed in the movie as a worldly man, deeply invested in the cultures of the world and it could be assumed well informed of the politics of the day. It stands to reason that someone like him whether he personally cared for Wilhelm or not wouldn't want something with the power of "The Heart of Atlantis" to fall into the hands of any war machine, let alone one he likely would have seen as the aggressing party.
Jeanette Keith (2004). Rich Man's War, Poor Man's Fight: Race, Class, and Power in the Rural South during the First World War
Barnes, Harry Elmer. The Genesis of the World War