ok, that is a new one to me. It doesn't make sense mechanically though. The valute on some pumps can be repositioned but the direction of flow through an impeller is most efficient from center to circumference. With curved vains, the opposite rotation will scoop water from the outside and compress it to the center, but not at the same efficiency as from inside to outside due to the weight of the water. Water is heavy stuff and the faster it is rotated, the greater the force pulling it to the outside. At low speeds, a flip floped impeller will seem to work but as the speed is increased, the pump efficiency will approach zero, and then the direction will be reversed again. You will find that most powerheads and pumps for aquariums will have flat vains. I do not know if the brands you are specifying are reversible. If you already own them, take them apart and look inside.
It is best to figure out how to use a powerhead in the proper direction i.e. with addapters.