Welcome to the forum
. Sounds like an interesting system and a good cause. I can see a few problems with trying to do this is South Dakota because of the cold winters. Hopefully they'll be heating the greenhouse if that's where it's located (On a sunny day there it can probably still get up to the 80's in a greenhouse but gets very cold at night and on cloudy days). They might need some artificial light to extend the growing season since they'd be pretty far north and won't have enough light (roughly 10 hours per day or more is needed) from early November to early February (you could still just harvest what was already planted and had grown, it's just tough to get growth with low day lengths). I have found that my AP system warms slower in the spring than raised beds but extends the growing season further into fall - raised beds and AP make a good combination.
If you want to shut down the greenhouse for the winter but keep the fish tank going, the fish tank should be located where you can keep it warm enough and set it up as a Recirculating Aquaculture System.
Cheers