How successful do you think these measures would be in the long run?
Not that much. I think it would be quite skin deep. Was the average German super devout and ready to go on the barricades when the government attacked the churches? Definitely not, but most Germans still saw themselves as Christians in one form or another.
When the Party tried to impose heavy-handed anti-church measures, such replacing crucifixes in public spaces with Hitler's image, it sparked protests in places. Public disapproval was high enough that Nazi party bigwigs backed off in 1941. Of course, they did this because they had a war to win and thus couldn't afford public discontent. But it's still pertinent.
In the case of the Wartheland, Greiser's anti-church policies were ironically at odds with his 'Germanisation' policies. His fiefdom was majorly Polish, he wanted to get Poles out and colonise it with Germans, but the measures such as these were a turn-off for Germans he was trying to persuade to settle there.
Moreover, whatever they seek to replace Christianity with will be rather...bland. It's Himmler's poorly articulated pseudo-pagan cultism, or, I guess, Hitler cult on steroids. The most hardline enemies of the churches - Himmler, Heydrich and Bormann - aren't exactly charismatic. And Rosenberg is utterly irrelevant. The most successful result would be a lot of resentment, with the clergy being controlled via bureaucratic measures, with church dogma tainted by Nazi tenets and churches infiltrated with police agents instead of the full-on introduction of whatever weird cultism they come up with. If they go full Cultural Revolution it wouldn't go well.
The reason the Nazis got as far as they did, among other things, was that they potrayed themselves as 'defenders of the occident against godless Bolshevism' and successfully coopted established institutions in German public life. The Confessing Church opposed their attempts to Nazify Christian theology...but didn't condemn the 9 Novemver pogrom. Dietrich Bonhoeffer was an extremely rare and very courageous exception. An open witch hunt would cause discontent and threaten stability.
Not very. Given that Himmler's mythology reads like a bad D&D campaign and is blatantly heathen to the Christians. If there's still a Pope somewhere outside of Nazi control he is bound to denounce it. I imagine that its at best skin deep and if Nazi control extends to areas where Islam is the dominant religion things are likely to get nasty very quickly, of course given the Nazi attitude they may have gotten bad already if the Nazis decide that all Semitic peoples are subhuman.
Nazis didn't view Arabs in the same manner as Jews. As early as 1935 the Ministry of Propaganda was instructing the German press to avoid terms such as anti-Semitic in favour of anti-Jewish since Semites included Arabs. This instruction was reiterated by Goebbels in 1942, when the Ministry's Anti-Semitic Action was renamed the Anti-Jewish Action. Later even the Racial Policy Office of the NSDAP came around.
Himmler and Hitler expressed admiration for Islam, but it was full of Orientalist cliches and basically a projection of Nazi 'virtues'. Himmler's view seems to have boiled down to: 'Islam is great because Muhammad had the smart idea of promising paradise, wine and women to martyrs. This is perfect for a soldier because then he doesn't fear death. Thus it's a good religion for a race of manly men. If only our ancestors had embraced Islam instead of flabby Christianity.' This seems to have been echoed by Hitler. There's an anecdote where he supposedly says it would have been better if the Arabs had won at Tours (or maybe it was the Ottomans at Vienna, either or), but then follows this up by saying that, of course, Muslim Germans would have ended up dominating them due to being 'superior'.
Funnily enough, in 1943 Himmler asked the RSHA and Gottlob Berger if there were any passages in the Qur'an that could be used for manipulative purposes to galvanise Muslim support in North Africa and foment a Mahdist revolt by depicting Hitler as a prophesied saviour such as the Mahdi. They came up short, but apparently the propaganda ministry printed a million copies of an RSHA propaganda pamphlet saying Hitler was a returned Jesus who'd come to slay the Jewish Dajjal for this absurd, quixotic effort. It's as stupid as it sounds. Funnily enough Muslim SS units got imams while their German SS comrades had to do without Christian chaplains.
Nazi Germany - not just some elements in the Heer - made an effort to win over Muslims in North Africa, the Balkans (an SS unit composed of Bosnian Muslims) and in the occupied territories of the Soviet Union. But, for starters, they only had limited access to Muslim populations. Central Asia is far away. Moreover, as with the Kaiserreich's failed efforts to incite jihad in World War One, their view of Muslim groups was incredibly stereotypical, since they lumped them together as a monolith, which led to a lot of bloviating about how Germany was Islam's one true friend and how Muslims should rise up against the 'anti-Islamic' allies.
Moreover, their promises remained rather shallow - and one imagines the locals noticed this. The Crimea was supposed to be colonised, and while the plans for the Caucasus were less set in stone than say the Ukraine since 'Aryan warrior farmers' were not supposed to settle there, it was meant to become a colony of some form under a Reichskommissar. So they'd only really offer token concessions, but no real independence. And North Africa was supposed to be Italy's playground and most of it was ruled by Vichy France. When the Grand Mufti of Jerusalem met Hitler in the Reich Chancellery, they exchanged platitudes, but Hitler wouldn't commit to an independent Palestine, and only promised to get rid of its Jews.
