Double Subverted: ... At least, that's what the magician wants the Allies to think.
Parodied: The Sealed Evil in a Can the Nazis are trying to magically evoke turns out to literally be pulling a rabbit out of a hat.
Zig Zagged: Those Wacky Nazis release the Sealed Evil in a Can in order to gain an edge against the Allied forces, however it turns out said evil has an army of minions, thus creating an entire new faction for the war. The Allies, upon bribing the entity, convince it to join them. Finally, it is revealed that this was an elaborate scheme created by both the Nazis and the entity to take down The Allies from the inside..... and the entity fights the Nazis.
Averted: There's no magic; the Nazis fight as they did in Real Life.
"Nazis by themselves aren't scary! Give them an alliance with demons!"
The author is very interested in the Real Life occult links the Nazis had, but doesn't feel that by themselves this would be an interesting story so decides to exaggerate them.
Lampshaded: "According to these reports, the Nazi high command have been meeting with powerful figures in occult circles with increasing frequency; Intelligence believes that some form of supernatural or paranormal attack is imminent. That's where you and your team comes in, Colonel."
Invoked: A powerful neo-Nazi necromancer approaches the Nazi High Command offering his services.
A group of white magicians opposed to Nazi Germany work in secret to ensure that any black magic or practicing magicians who could help the Nazis are dealt with before the Nazis can approach / use them.
Hitler scoffs at the proposal his occultist underlings have prepared for him about using necromancy to win the war and dismisses it outright.
"The first time anyone tried summoning this demon was in Germany 1945, as the Russians approached Berlin. It was also the last time; every single member of the SS unit involved died. Horribly."
"You're summoning demons? I don't understand! That's impossible!" "Zen ve vill hav to make you understand, Herr Colonel..."
Conversed: "Oh look, a story about the Nazis summoning demons again." "Well, they did have lots of ties to the occult..."
The Nazis might be able to summon powerful supernatural forces, but this does not equal being able to control them; the Nazis soon find themselves on the losing side along with the rest of humanity as their rituals backfire on them.
In something similar to what happened in Real Life, the Nazis throw so much time, effort and resources into supernatural projects — many of which go nowhere — that they neglect their conventional forces, meaning the Allies still have an edge that enables them to win the war.
The Nazis specifically seek out a supernatural entity which shares their ideology and / or which they can easily bind and control.
Nazi necromancy, while time consuming and resource-intensive, is still powerful and formidable enough to give the Allies a hard time.
Played For Laughs:
The Nazis intend to defeat the Allies by impressing them with the kind of conjuring tricks you'd find performed at a child's birthday party. The Allies take it seriously. "My God...there could be Rabbits the size of Elephants in that hat! And if he can remove his own thumb, he could remove ours as well! Game Over Man!"
The single zombie the ritual managed to awaken walks up to the Nazi Necromancer, gives him a wedgie, and goes back to being dead.
The Nazis summon what could have been a Cosmic Entity... under two feet tall.
Played For Drama: Allied Intelligence learns that a top-secret Nazi project has been established to summon a powerful Eldritch Abomination that they will use to create a Third Reich that will never end, and must assemble a crack team to prevent this before the Nazis succeed and bring about a thousand years of darkness, or even The End of the World as We Know It.