They can....but it is tight. My ducks aren't even a large breed. If I could have put a bigger one it would have been nice for them.
Their space was already fenced when I finally got to the pool.
A thing to consider is how often it will need changed (they muck it up quick) and water cost/availability. I change it every other day in summer. Winter....no pool cause I am carrying jugs of water since the hose freezes for weeks on end.
The rubbermaid tanks are floating deicers only. I don't think that will work for a small pool and active ducks. If I had to have a deicer I want a sinking one and a bigger tank.
At 50 gallons my seven ducks get less than 10 gallons per duck to muck up. That is a really small amount of water really.
Go bigger if possible. While mine don't complain I know bigger would have been nicer.