Fishtailing depends on shafts, propellers, and rudders

Is the fishtailing or oversteering shown in Ultimate Admiral: Dreadnoughts a real ship-handling effect?

To an extent; the effect depends on the combination of shaft torque, propeller number and geometry, shaft length, and rudder design.

A warship does not turn through rudder angle alone. Shaft torque and the number and placement of propellers alter the flow reaching the stern. Propeller size, shaft length, and rudder geometry can then make a ship overshoot or oscillate around the desired course. Fishtailing is a real effect, but its severity depends on the particular hull and propulsion arrangement.