So, I recently found out about how the Main Cathedral of the Armed Forces in Russia maintains a section containing Adolf Hitler's hat and uniform as relics within a wing of its building. Since it's my understanding the Catholic and Orthodox churches only maintain relics of the saints, does that mean that the Russian Orthodox Church recognizes Adolf Hitler as a saint? Can someone go to visit the church to see Hitler's hat and pray for him to pray to God on their behalf? If they don't regard Hitler as a saint, then why do they maintain his relics?
Does the Russian Orthodox Church recognize Adolf Hitler as a Saint?
The short answer is no.
There is no liturgical celebration for the above said person known infamously as Adolf Hitler in the Russian Orthodox Church.
I can find no glorification process for him either.
The fact that the Main Cathedral of the Armed Forces in Russia maintains a section containing Adolf Hitler's hat and uniform as relics within a wing of its building is in a sense not surprising.
For example, many Catholic Churches in Italy, have museums attached to them, say in an adjacent wing just outside the church (proper) or in or around the cloister if it Church was at one time a monastery or convent. All sort of the ”museums” exist throughout Rome. It is not a new idea.
Many of these church museums in Italy are by paid admission only, but not all.
Seeing that this is the Main Cathedral of the Armed Forces in Russia, it does not seem so out of place that there exists in a wing of the building a section dedicated to World War II memorabilia. Referring to Hitler’s personal effects as relics (given the situation) is a poor choice of words. A better phrase might have been chosen such as historical artifacts or something similar.
The website you link to clearly states that Hitler’s personal belongings are housed in a separate military museum (with historical military paraphernalia) area within the complex, thus not in the actual worshiping section of the cathedral.
The cathedral complex also houses a museum section, housing Adolf Hitler’s personal belongings, including his uniform and military cap. - A giant BLACK cathedral from remelted weapons appears in Russia
As such, certain aspects of the design of the cathedral have proven to be controversial.
At the end of April 2020 photos were leaked which showed in the unfinished cathedral mosaics of Russian President Vladimir Putin, Defense Minister Sergey Shoigu and other high-ranking Russian officials, as well as Joseph Stalin. The Russian Orthodox Church initially explained the presence of mosaics featuring Putin and Stalin according to the tradition of depicting historical events – in this case, the 2014 accession of the Crimea to Russia and the Great Patriotic War (World War II). However, later it was reported that the cathedral would not have any mosaics of Putin. The Russian Orthodox Church explained that this decision was made taking into account the President's own opinion.
Caveat: I am not a Russian Orthodox, but I believe I have answered this question in a spirit reflecting their own perspectives on this subject matter.