Based on the design of stepper motors, having no exposed electrical parts, is it then conceivable that they will work submerged in water or other fluids?
Unless the bearings have waterproof seals , the bearings will rust.
Disk drives use ferro-fluidic seals to seal out all air.
So you cant simply use ANY stepper motor because there is no commutator. But they do exist. Oil filled double O ring steppers. http://www.empiremagnetics.com/prod_wat/prod_wat_stepper.htm
It will work if you have an underwater stepper motor!
Most stepper motors are not designed for underwater use, and if it doesn't say so in the datasheet then you must assume that it won't work.
Just because the motor does not appear to have exposed parts doesn't mean water can't kill it. Motors have seals and bearings that water can get into and destroy. The lubricants used on the bearings don't always work with lots of water. The motor shaft and bearings can rust. Etc. There are lots of ways that water can damage a stepper motor.