Catalyzes the NADPH-dependent reduction of scyllo-inosose (SIS) to scyllo-inositol (SI) in vitro, but is unable to dehydrogenate scyllo-inositol and myo-inositol. Is less efficient than the functional paralog IolW. Under physiological conditions, may primarily function as an NADPH-dependent oxidoreductase that reduces carbonyl group(s) in its substrates. Cannot use NADH instead of NADPH. NADP(+) + scyllo-inositol = H(+) + NADPH + scyllo-inosose Is not induced in the presence of scyllo-inositol or myo-inositol. Belongs to the Gfo/Idh/MocA family.