Some of them have a defrost feature now - you can find examples here - but not all convection ovens have this. For instance mine is about 7 years old and it doesn't.
Can A Convection Oven Defrost Food?
I'd have to say no, since a convection oven is similar to a regular oven except that it has a fan behind the oven cavity that circulates the heated air throughout the oven and over and around the food that's cooking. So it usually will cook things faster and brown things better. Stick to the microwave for defrosting.
Yes, on low but I do not recommend it.