I don't think Hitler understood Nietzsche at all. For example, Nietzsche absolutely loathed the common antisemitism of the German people and once expressed his wish that all German anti-semites should be rounded up and excecuted. So Nietzsche would clearly have hated the Nazis. He was even so ashamed of being a German and the bigotry of Germans that he often claimed to be a baron Polish when he travelled around Europe. He also broke with Wagner due to Wagner's fascination with German nationalism and instead began to listen to French opera and composres like Bizet. So I don't see any connection between Nietzsche and Hitler (it is true that Nietzsche had a sister who became a Nazi after Nietzsche died, but she definitetly did not understand what her brother had written before he died, so the sister had nothing to do with his writings).
What interested Nietzsche with Zarathushtra was not his theology (which by the way does open for the interpretation that we are if not gods ourselves then at least definitely potentially godlike, which is the Zoroastrian concept of "ahuravatat") but his ETHICS. Nietzsche was opposed to the MORALISM of Judaism and Christianity and what fascinated him with Zarathushtra was that Zarathushtra preached an ethical rather than a moralizing system (what happens is always a result of causes and effects and never a result of divine intervention, as it is in Christianity). Nietzsche wrote about this himself in "Ecce Homo", his biographical text which he published after "Also Sprach Zarathustra". This is is where he refered to Zarathushtra as "the father of all ethics" and Spinoza as his "brother of ethics". Which explains why Western converts to Zoroastrianism often come through studies of Nietzsche and Spinoza first.
I hope this clarifies the issue so that we get the Zarathushtra-Nietzsche connection right. Hitler never spoke of Zarathushtra at all and never read any Zoroastrian scriptures. Actually he didn't read much books at all. So let's just be a little bit careful with connecting Hitler with Zoroastrianism or Western interest in Zoroastrianism. There seems to be no historical connections whatsoever.
The way I have come to view this issue is such:
Zartosht the first person in history that discovered the One God,
Ahura Mazda, Spread his knowledge in order for people to discover God
forthemselves, by giving them directions instead of manipulating them
with miracles or brainwashing Leaders to force their beliefe on
others, I will not go further by naming historical figures.
Zartosht believed that there was One God, and that the Universe he
created; Perfect. We just need to discover it and become a part of it
and manifest Gods creation in all walks of life. We should aspire to
achieve Perfection in our lives Being next to God in his creation,
instead of fearing him or being "Goul-oriented"; Heaven and Hell.
That is tabood in the west, more or less; "nobodies perfect".
We don´t need Priests, Rabbis or Mullas to talk to God, He is always
present; we just need to open our eyes.
We are all perfect right from the start; however we happen to be or
look like with all our flaws; it´s the flaws that makes us perfect;
thei´re there to remind us that we should focus only on the blessings.
Nietzche, in my opinion, misunderstood Zartoshts teachings, and saw
zoroastrianism as a kind of zen buddism for example where we become
Gods, this is not what Zartosht preached; We can only take part of
Gods creation or become One with God, not become Gods ourselves.
Unfortunately there are those Zartoshties that believe the latter.
Nieztches Zarathustra sais "God is Dead" and "We must take the leap
into being Supermen"; With other words: Elevate ourselves beyond good
and Evil. The God Niezche talks about is the Abrahamian God;God;
Jehova; Allah. So we could interpret it that he means: if Zarathustra
lived today he would claim that This God The Biblical one is dead; but
nonetheless this can be misunderstood.
And So we come to Hitler, who misunderstood Nieztche further; The
Superman; the Supreme race.
No Iranian believes himself to be of the supreme race; We are Aryans
and very proud of this, but never intolerant of other beliefs or
cultures, and History is the witness of this.
So I see the whole Nieztche, Hitler association as a big cultural
crash between, Well Lets Call It; East and West.
Of course the similarities over weigh the differences.
In hope of a brighter Fuiture
All the Best