Can German Potato Balls be frozen?
Yes, you can freeze them: I have done it before, and it works just fine.

They key (in my experience, that is) is to freeze the balls quickly if uncooked, and put them into the boiling water still frozen when you actually do the cooking.

I have also been freezing cooked potato balls, and that works just fine as well -> In that case, warm them up in hot, but not boiling, water.

A note due to the comment below: The recipe I use calls for half cooked, and half raw potatoes, with the raw half being pressed almost totally try of water; and they DO fall apart if I do not take that part seriously. So, except for potato-flour added again, there is not that much raw potato starch left when I freeze them.