Regarding Germany's reaction to Vagner's Aryan Brotherhood. It's indeed comedic how Vagner's attempts to make contact with the Third Reich falls on deaf ears as they just ghost on him in their immense confusion at this peculiarity bordering them to the east. Yet the fact that the AB does border them to the east has me thinking that truthfully, Germany can't be able to just simply pretend that Vagner isn't there, through his conquest of West Russia all the way to the conquest of Siberia, because Vagner could just simply send some delegation straight to Moskowien in an effort to establish relations and the Fuhrer would, whether he likes it or not, then be forced to respond in some way which nonetheless acknowledges that these guys do exist. Furthermore, it's also a matter of simple geopolitics. Considering that it was a threat from West Russia which had thrown Germany into a huge crisis in the 50s', I'd imagine that a great deal of attention would be drawn to that area.
Now, of course there is the question of how Germany would exactly react to the AB. I'd imagine Bormann for one would find the whole LARP spectacle as half-parts laughable and deranged like we all do yet I also think that he would be cognizant of the fact that the AB's geography makes it a barrier to German East Europe and a buffer zone against the Russian unifiers east of the Urals. I therefore believe that while he'd keep the AB at arms length, Bormann would go out of his way to provide help by way of supplies and weapons to aid Vagner's campaign in bringing the rest of Russia under heel as it would simply be in the Reich's self-interest that no antagonistic entity exists on the Moskowien border to repeat the WRW all over again.
Speer and the GO4 would be interesting. Since on one hand they would absolutely abhor their policies of mass enslavement which stands in contradiction to their policies as well as the wariness of bad optics of associating themselves with such as regime but I can imagine a couple ways that Speer and the GO4 would fiercely butt heads on. On principle the GO4 may not want anything to do with Vagner whatsoever (which makes TNO2 interactions between GO4 and the Russikiy Reykh interesting) yet Speer himself may hold views similar to that of Bormann while also making encouragements to Vagner to phase out the slavery and tone down the pretty egregious brutality. Not only because Speer would want a stable ally within Germany's sphere that can keep the Russians off Germany's back but also so that he can build up the sanitized image of himself that he propagates through justifying his alignment with Vagner as a moderating influence on the AB that is doing away with the excesses.
As for Goering (in his current depiction before V&J), being one of the more pragmatic thinking Nazis, he and Vagner might come to an agreement that would see the Russikiy Reykh annexed as an RK but with Vagner himself as Reichskommisar. Schorner of course is a war-monger but if presented with an opportunity to simply take over a large piece territory without having to fight it out and no loss or compromise on his side, he might just take it.
The gist here is that however Germany regards the AB, I think it would be clearly recognised that their existence provides a bulwark to the possibility of Russian resurgence that would see Germany's gains on Eastern Europe decisively secured within their grasp which isn't something that can just be ignored. Additionally, developing relations with the Russikiy Reykh could be recognized as most likely granting Germany free, unfettered access to exploit the vast treasure trove of Siberian resources as well as geographically allowing power projection into Asia, especially Japan's CPS. The AB's usefulness would be hard for the Fuhrers to ignore, whatever their personal thoughts towards them.