Yes, there are a lot of rumours that Imperial Palace owner Ralph Englestadt, now deceased, was a Hitler & Nazi memorabilia collector. And apparently the rumours are true. But I think he was misunderstood about the reasons why he collected those items. It wasn't due to approval of Nazism, but more due to the historical significance (though grisly) of Hitler the person. Even if he was a rotten person, no one can deny Hitler's prominence in human history. And that's what fascinated Englestadt.
By the way, anyone familiar with the University of N. Dakota would know that Englestadt was by far the biggest benefactor that UND ever had. They now play their hockey games in Ralph Englestadt Stadium, and he donated hundreds of millions to UND over his lifetime, and through his estate.