Dehydrogenase involved in the biosynthesis of oxogeranial from hydroxygeraniol, a precursor of the terpenoid indole alkaloids such as vinblastine and vincristine. (6E)-8-hydroxygeraniol + 2 NADP(+) = (6E)-8-oxogeranial + 2 H(+) + 2 NADPH Present in seedlings and vascular tissues (at protein level). Restricted to the epidermis. The recommended numbering of geraniol gives (6E)-8-hydroxygeraniol as the substrate rather than 10-hydroxygeraniol and (6E)-8-oxogeranial as the product rather than 10-oxogeranial as used in most publications. Belongs to the zinc-containing alcohol dehydrogenase family.