In general, if a motor
hums it is seized for whatever reason. I suspect if you were able to free up the motor
shaft it would probably work just fine as is.
Sometimes they can be satisfactorily freed up just by turning the motor shaft a few times, but each individual situation is different so it is only a guess I'd try that first on your boat. If you can see the impeller sometimes you can just give them a few wiggles with a long skinny screwdriver poked in between the baffles. Others require disassembly obviously.
When you have it freed up or replaced, as part of a weekly routine flipping the switch on for a second will keep it from locking up from misuse.