Viburnums tend to be self sterile, which means that pollen from a flower will not fertilize the ovules of that flower. This would be the general consensus, however, some species and cultivars have a lesser tendency toward self sterility, while a few are actually thought to be self fertile. With this being said, for best fruit set, another seedling or clone of the same or closely related species should be planted nearby for best fruit set. Much emphasis has been placed on the lack of fruit set of V. nudum so suppliers have offered a pollinator. Even though you are purchasing a plant labeled V. nudum pollinator, there is no actual clone, variety, or cultivar of that name. In actuality, any other nudum can act as a pollinator as long as it is not the same clone and it is blooming at the same time. This would also be true for V. dilatatum, V. dentatum, etc.