Hydroxylase involved in the biosynthesis of hydroxygeraniol, a precursor of the iridoid monoterpenoid swertiamarin. (2E)-geraniol + O2 + reduced [NADPH--hemoprotein reductase] = (6E)-8-hydroxygeraniol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Expressed in leaves, stems and roots. Up-regulated by methyl jasmonate treatment. The recommended numbering of geraniol gives (6E)-8-hydroxygeraniol as the product rather than 10-hydroxygeraniol as used in most publications. Belongs to the cytochrome P450 family.