Q:

How are ocular dominance columns monocular despite binocular complex cells? 

Orientation columns in the primary visual cortex are known to have (mostly) simple cells in layers 4 and 6, and (mostly) complex cells in layers 2,3 and 5.  Orientation columns spanning an entire range of orientations (0-180 degrees) are “grouped” into ocular dominance columns. 
My question: Ocular dominance columns are monocular columns, corresponding either to the contralateral or the ipsilateral eye.  Complex cells, however, are binocular.  How do these two things go together? 

A:

Ocular dominance columns are not purely monocular, nor are simple cells purely monocular. 
Simple and complex cells both exhibit a range of ocular preference, from preferring one to the other.  See this figure from Hubel and Wiesel, 1962:

Hubel, D. H., & Wiesel, T. N. (1962).  Receptive fields, binocular interaction and functional architecture in the cat's visual cortex.  The Journal of physiology, 160(1), 106-154.