Eh? I'm not so sure the Germans had long standing designs on Ukraine, Belarus & the Baltics, ideas of a''drang nach ost'' had a lot of support and the Kaiser's men kept it up OTL even when Germany faced utter ruin on the Western Front.
Belarus? Chortle. Pretty much everybody considered Belarus an integral part of Russia, including the Russians, the Germans, and the Belarusians. Almost nobody would have thought about detaching it from Russia before the war. Ukraine is the same, but less, and while German nationalism did have a fascination with Estonia and Latvia, they were not occupied in 1917, and Russia was unlikely to give away provinces so vital to the security of its capital from any decent negotiating position.
That was what Russia lacked at B-L. What had already happened was that Trotsky, for reasons which I myself do not fully understand, had walked out of talks where the Germans offered much the peace I describe, adapted to a military situation that had turned further against Russia and ordered his forces not to resist the Germans in any serious capacity. The Germans had then advanced recklessly, since no-one was stopping them, and so occupied Latvia, Estonia, and much of Ukraine and Belarus. There they ran into provisional governments (run of the mill Radas with strong regionalist parties in the Slav lands, local German councils in the Baltic) who were willing to sign deals with them to escape from the looming Red Army, who had already captured Kiev, from which the Germans expelled them. Trotsky eventually had to sign a peace treaty which put a stamp on the new situation on the ground by rneouncing sovereignty over those area sthat Germany had occupied and installed puppet governments over. The whole thing was rather bizarre and flukish and certainly not a long-contemplating German scheme.
Who were the "Kaiser's men" anyway? In fact, the Kaiser was the general's man, and the generals were throughly pragmatic and had no interest in continuing the war in the east for a reason that was ideological rather than strategic.
And how did they "keep it up" when Germany "faced utter ruin"? The German army disintegrated
after Brest-Litovsk. It was the end of the war in the east which set the stage for Germany's last throw of the dice in the west, and her subsequent collapse.