Two totally different animals. Impeller is rubber/neoprene, 6 straight blades, propellers have rake, pitch, diameter, cup, plastic, aluminum, stainless steel, composite, bronze, steel, lots of variables according to use and application. Good Luck!
Being that he asked about impellers on the PWC forum - he's probably referring to the swirly piece of metal that propels water through the jet pump thus making a PWC move forward.
if we're talking outboard engines - then yes, the water pump impeller is neoprene or rubber.
yes, impellers have a pitch like a propeller, and yes - different pitch impellers provide performance in different areas of the power band depending on the application you are using it for.