First, it is difficult to overstate the diligence of the US in absolving the Showa Emperor of the war. To all the world, General Tojo was the vile warmonger prime minister responsible for every atrocity. When Tojo went slightly off script during his trial for war crimes, the prosecution stopped so that he could be set back on the right narrative path. For decades, the official story was that the Prime Minister and his cadre of fanatic nationalists started the war against the Emperor's wishes. The CIE, the US propaganda department during the occupation, even wrote a movie about the Emperor's brave struggle to end the war (though the film project eventually fell through).

It is therefore difficult to conceive of any US presidents recording any thoughts of blame or ill will toward Hirohito. I suspect that even privately, it was decided not to make mention of such feelings. Maintaining the myth of the blameless Emperor was considered paramount to the success of the occupation and the rebuilding of Japan as a powerful American ally in the otherwise communist east.

Note that in Ford's remarks on the occasion of Hirohito's visit to the US, wherein he discusses the history of the relationship between the two nations, the President doesn't even mention the war. At all. http://www.presidency.ucsb.edu/ws/?pid=5298

I cannot say whether President Ford privately blamed Hirohito for the war but if he did, he would never let it be publicly known.

This was actually part of the topic of my (aborted) dissertation work during a previous career. While it's true that the emperor was part of the propaganda of WWII, and there was much discussion of the "fanatical" worship of the Emperor as a god and that it might be necessary to simply wipe out Japanese culture from top to bottom in order to make the world safe, the counter narrative of Emperor as figurehead was also somewhat present during the war and came to the forefront as the war was entering its final stages in 1944-45.

At that point, it was already becoming apparent (particularly by 1945) that the Soviets had no intention of letting go of at least some of the territory they were controlling as they advanced toward Germany. The Soviets were committed to entering the war against Japan once the European war finished. The US actually wanted to wind things up before that happened.

The powers that be in Japan were equally fearful of the Soviets and there is one line of thought that says fear of the imminent entry of the Soviets into the war in August 1945 had as much if not more influence on the decision of Japan to surrender.

What does all this have to do with the emperor? The US also recognized that tearing down Japanese society and rebuilding it from the ground up would be dangerously destabilizing and allowed the Soviets or other Communist groups a chance to get a foothold just as was happening in other places.

If the emperor is just a figurehead, he does not have to be removed and can remain a symbol of continuity even as the militarists and people held responsible for the war were extirpated and the Japanese government restructured. The emperor meeting with General MacArthur and appearing at various points as the Occupation of Japan proceeded implied continuity and the emperor's endorsement of what was going on.

That is pretty much the view of the emperor that took hold in the US after the war, particularly as Japan was no longer a military threat and appeared eager to rebuild in a Westernized appearance. It remained important to have a close relationship with Japan throughout the Cold War because of the closeness to "Red China" as well as the eastern part of the USSR. Japan was very important as a military base for the US as well as a "bulwark" against the further spread of Communism, remembering the fear of falling Asian dominos.

So I don't think it was a big stretch for any of the postwar US presidents to have dealings with the Showa Emperor afterwards as he had largely been absolved of responsibility by the postwar reconstruction and in the postwar period had indeed acted pretty much as the ceremonial figurehead he was supposed to be. I think meeting with him was pretty much seen as a diplomatic and formal yet ultimately meaningless gesture much as hosting visits by British royalty is.