  We present high spatial resolution H and K'-band images of a complete sample
of ultraluminous infrared galaxies selected to have warm mid-infrared colors
known to be characteristic of active galaxies. The extended underlying galaxy
is detected in each system, as are tidal features and many of the star-forming
knots seen at optical wavelengths. While some of these knots have a
considerable near-infrared excess, we show that they are likely to have
bolometric luminosities more similar to that of the extended starbursts with
similar optical morphology seen in less far-infrared luminous interacting
systems. We find that each ULIG has increasing contributions at long
wavelengths by a very compact source which we identify as an active galactic
nucleus. We show that the optical/near-infrared colors of these putative nuclei
are much more extreme than the most active starburst IRAS galaxies, yet are
identical to "far-infrared loud" quasars which are in turn similar to optical
quasars combined with large quantities of hot dust. Half of the ULIGs have
nuclei with dereddened near-infrared luminosities comparable to those of QSOs,
while the other half have dereddened luminosities more similar to Seyferts,
although this may be an effect of patchy extinction and scattering.
