It is not unheard of for a washing machine to drain into a sump pump. This was probably done when the owner of the home wanted the machine in the basement but didn't want to pay to have it plumped correctly. It is not recommended.
sump pumps are there to remove water that comes into a basement from outside. This is usually a fairly uncommon situation and the amount of water removed at any one time is generally a lot smaller than the amount that comes all at once from a washer. In addition, if you use hot water this is again something outside design.
If your washing machine drains through/to the sump pump, you should be very worried if the sump pump is off or broken and you use the machine. Of course, if you know it is off and still use the machine, that makes you an idiot!
