I am reading the description of Paph hookerae and Paph volonteanum in a book called "The Genus Paphiopedilum Natural History and Cultivation" volume 2 by Dr. G. J. Braem.
Paph hookerae: "The leaves of Paphiopedilum hookerae are elliptic-oblong, deep reen, distinctly tesselate with grayish-green to yellowish-green, and the undersurface often is suffused with red." quote pg 279. The 2 pictures of Paph hookerae only have a notch at the bottom of the staminode, there is no upper notch.
Paph volonteanum: "In general, the description under Paphiopedilum hookerae can be followed. The leaves are proportionally narrower and spotted purple on the underside, the petals are broader and more obtuse, and te lip is more constricted below the orifice. The petals are about 1 inch (2.5cm) wide, bright purple at the apex, and intensely spotted with purple toward the base. Paphiopedilum volonteanum, however, is a highly variable species occuring over a vast range of altitudes " P284
Within this complex, two taxax, Paphiopedilum hookerae and Paphiopedilum volonteanum, have been described at the species level. There is no doubt that the two concepts are very closely related, and most authors have hitherto treated them as two varieties of the earlier concept, Paphiopedilum hookerae. The same view is taken by the registrar of orchid hybrids at the RHS. The judges of the American Orchid Society have not been consistent in their treatment. Some plants of Paphiopedilum volonteanum have been awarded as such while others were awarded as Paphiopedilum hookerae var. volonteanum. The differences between the two taxas are indeed very subjective, especially in view of the fact that Paphiopedilum volonteanum has proven to be extremely variable in respectto the shape of the petals, lip, staminodal shield, and the characterstics of the leaves. Some low-elevation population of Paphiopedilum volonteanum show leaves that are as broad as those normally considered typical of Paphiopedilum hookerae and have purple markings underneath only at the base. This variation is not surprising considering that Paphiopedilum volonteanum occurs from 200 ft (60m) to 7500 ft (2300m)." pg277
Sounds like you cannot easily distinguish the differences. Sounds like even in the wild, Paph volonteanum and Paph hookerae can probably pollinate each other and you cannot tell.