I don't think there is a single standard for Go Kart wheels, and I also don't think there is a single standard for wheelchair motors.
You need to measure the diameter of the output shaft of the motor (or better, look it up in the datasheet!) and compare to the diameter of the hole in the hubs/rims. If they don't match, you need a coupling of some sort. There are tons of different kinds of couplings, and for experimentation, many people turn their own on a lathe to boot.