You may not be implying this, but just for clarification: the oxidation of hydrogen is not a significant energy component in NiMH or NiCd batteries. The energy is obtained from the metal, not the hydrides. Electrolysis in those batteries, is, in fact an unwanted byproduct of overcharging or catastrophic discharge. Excess Cadmium and other technologies are used to bind the excess hydrogen in the electrolyte to the metal, but it is an unwanted artifact, not part of the energy mechanism.
As you're probably aware, neither of these technologies is a state-of-the-art energy density solution. Li-Ion has higher density, and Li-Polymer is higher still, and these storage media don't have the problems that hydrogen has as a storage material.