Your dealing with a few things here. First is starches in general. The thing to know about starches is how they gelatinize and at what temperatures.
This powerpoint is a nice primer on that topic. www.cfs.purdue.edu/class/f&n630/gelatinization.ppt
Basically your dealing with amylose and amylopectin, together they are what we know as a starch. When they come in contact with water the starch cells begin to swell and when their gelatinization temperature is met they burst and release their contents into the medium they are in. In the case of a dough ball, your dealing with tons and tons of little cells being held together loosely at first by the physical pressure of kneading them into balls and then when the heat causes the starches to gelatinize they adhere to one another kind of like being caught in a net.
Now the fluffiness portion of the question can really depend on how the dough is being cooked. For something like a dumpling being cooked in the boiling water, one would typically want to work the dough as little as possible to avoid making it too dense and if using flour to lessen the gluten formation that can make it very chewy like bread. Some recipes call for leaveners that can create gas bubbles when heated to a certain temperature and then through gelatinization the bubbles are trapped inside the dough and create an airy texture.
Par-cooking potatoes is an extremely common technique.
However, the shredded or grated kind of hash browns would be very difficult to par-cook with wet methods, as they would go to mush quite quickly if you tried to simmer them, and then you would have the trouble of squeezing out the water afterwards (which is necessary so they crisp up, and so they finish cooking rapidly).
Par-frying would be labor intensive, and not terribly scalable either.
Typically, shredded hash browns only take about 15 minutes to cook, which is not terribly long.
I have had some success with making shredded hash browns in a very hot (450 F, 230 C) oven, baking them for about 30 minutes. They are not quite as good as fried, but they are still good, and the technique would scale quite well.
If you are willing to experiment, I believe that par-baking them for about 20-30 minutes at a more moderate temperature (say about 350 F, 180 C) would be a promising approach. They would stay dry, and you could then finish-fry them just to crisp up and get some buttery flavor. You would need try it a few times to work out the be combination of baking and frying times.
Best Answer
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.