When it comes to German domination over eastern Europe, one has to take into account that Germany’s relations with the newly independent states carved out from the Russian Empire will differ from case to case. I think that German relations with Lithuania and Finland for example would have been pretty good, even if they were ruled by German princes. I also think that relations with Rumania could have been fairly decent, especially if the Germans grant Rumania Bessarabia (which means Rumania would have gained territory, despite being on the losing side).
Poland would have been more difficult, since Germany had a sizable Polish minority in the east. But I think German-Polish relations could be improved should A-H break up, since Poland would then most likely be allowed to annex Galicia. Estonia and Latvia would also be difficult, since they would not only be part of the United Baltic Duchy, but also had sizable German minorities which made up most of the regional elite.
As far as Ukraine is concerned, I think it mainly depends on its internal situation. If the Germans and their local allies manage to defeat the various Red and Black forces in the region, and some manner of stability is reached, then I see no reason why Germany and Ukraine couldn’t establish a decent relationship. It’s not like the Germans are keen on a permanent military occupation. They will probably want to establish some military bases, and make sure that eastern Europe stays in the German orbit economically. But other than that, I don’t think they would care too much about what Poland, Ukraine etc. would do domestically. Unlike the Russification policies that Russia pursued prior to WW1 for example, there would be no ‘Germanization’ or anything like that (unless you believe Germany actually planned to annex all of eastern Europe).
Also, not only could the Germans try to bring rebellious eastern European countries in line by pointing to the big scary Russian/Soviet bogeyman in the east, they would also have the option of playing the various countries against each other. There will likely be territorial disputes between Poland and Lithuania over Vilnius for example, or between Poland and Ukraine, which the Germans could exploit if necessary.
Overall I don’t see any reason why we should expect eastern Europe to share the fate it suffered OTL under the Nazis in the case of a German victory in WW1. I think a possible OTL comparison could be the relations between Russia and its former Soviet republics. Today most of them are still in the Russian orbit, and Russia gets along pretty well with most of them, though there are some cases where relations have turned sour (Ukraine, the Baltics and Georgia especially). I think it will be similar for Germany and eastern Europe: most eastern European countries will be fine with the new status quo, but there are some cases where there might be problems.