Catalyzes the reduction of succinate semialdehyde to succinyl-CoA. The enzyme is specific for succinate semialdehyde and succinyl-CoA, and only shows low activity with palmitoyl-CoA. There is no activity with NAD(+) as cosubstrate. Participates in the 3-hydroxypropanoate/4-hydroxybutyrate cycle, an autotrophic CO(2) fixation pathway found in some thermoacidophilic archaea. CoA + NADP(+) + succinate semialdehyde = H(+) + NADPH + succinyl-CoA Binds 2 Zn(2+) ions per subunit. Belongs to the zinc-containing alcohol dehydrogenase family.