Up to mid-1944 USSR lacked what was by far the biggest area of employment for Russian collaborationist units on German service - occupied foreign territory, where collabortionist troops could be used to maintain orders (Vlasovites didn't enter frontline service until mid-1984). And even after Summer of 1944 it would be extremely unwise to use some kind of collabortionist German force to maintain order in, let's say, Poland or Bulgaria. So, there's just no market to employ armed German units on Soviet side of the Eastern Front. Speaking about hiwi (volunteer unarmed helpers), there's very little research in this area, but Soviet war memoirs are sprinkled with references to German PoWs working as equipment maintenance specialists in air force, tank units, artillery, and other areas where services of good techns were in demand. Most likely, there were thousands of them.
On the flip side, Soviet Union did have a huge workforce problem in economic and infrastructure recovery, and that's where thousands of POWs were employed. And, condition-wise, it ranged from pretty tough POW camps to more or less "labour army" setups, when German lived in unguarded barracks and worked in construction, lumber industry and stuff like this under command of their own officers.