We investigate the origin of the huge luminosities produced by high-redshift SCUBA galaxies using the combination of ultra-deep X-ray observations (the 2 Ms Chandra Deep Field-North) and deep optical spectroscopic data. Even though a large fraction of high-redshift SCUBA galaxies host AGN activity (upward of 38%), we argue that in almost all cases the AGNs are not bolometrically important (i.e., contribute <20% of the energetics). Thus, most high-redshift SCUBA galaxies appear to be star-formation dominated. A substantial fraction of high-redshift SCUBA galaxies show evidence for binary AGN activity. Since these systems appear to be interacting and merging at optical/near-IR wavelengths, their super-massive black holes are likely to eventually coalesce.