The Nazis can't win OTL WW2. What's needed are Notzis with a similar, but not the same, war.
There are any number of ways my idea could work. Either, the state as such is pretty german friendly, maybe a few tens of thousands of germans stayed and became ukrainians (and helped it stay independent - For some delightful irony, they are motivated by the promise of a big parcel of land as their discharge bonus, Lebensraum style
- and or it's some sort of mildly fascist state that is paranoid about the USSR and bickering about the border with the Poles.
Even if we aren't talking outright alliance, certainly amenable to German ideas - Maybe a Poland is divided in three ways in this TL, and then they are de-facto forced to join in against the USSR (or very happy allies, either or) since if Germany loses, the USSR is there, and if Germany wins, well, that won't be nice for them either.
Or, WW2 starts when the 'Noble Hitler defends poor ukraine against the ruthless evil USSR' - (this would be the TL where France and the UK look away and pretend that the Poles weren't invaded to get at the USSR) until it's too late.
The only thing that really matters for WW2 and the Nazis is that the state (definitionally) won't be interested in being a part of the USSR, and consequently robs it of a lot of capital, industry, and resources - So even as a very democratic, very UK/France friendly state it would be very much to Germany's favour. (Dark idea - Maybe the Molotov ribbentrop pact in this TL lets stalin invade Ukraine, would be very naziesque to shove them into the fire and then 'rescue' them).
And of course, it's unlikely to be that - The allies were against secession from Russia, so the Ukrainians will remember that and the most likely regime is going to be very nationalistic, very anti communists - Well we know that that is. If we then add in the unavoidable border issues with Poland, as well as the almost automatic paranoia about the USSR, it's going to be a very German friendly nation. Even Hitler shouldn't be able to alienate them.