What is the relationship between migraines and histamine?
Yes, this is true.
Histamine is thought to induce the enzyme Nitric Oxide (NO) Synthase.  NO is then available to act locally on the vasculature as a vasodilator.
NO binds to guanylyl cyclase in vascular smooth muscle cells, which leads to the production of cyclic GMP, which in turn forms phosphorylated protein kinase G. PKG phosphorylates Ca2+ channels, slowing the influx of calcium into the cell, which leads to smooth muscle relaxation, and vasodilation, which leads to migraine.
The only silver lining is that there is a check in place: with the binding of histamine to H3 receptors on c-fibers in the central nervous system, feedback inhibition prevents the further release of histamine from these sites.
References:

Akerman S, Williamson DJ, Kaube H, Goadsby PJ. (2002).  The role of histamine in dural vessel dilation.  Brain Res. 956(1):96-102.
Gupta, S., Nahas, S.J.,Peterlin, B.L. (2011) Chemical Mediators of Migraine:
Preclinical and Clinical Observations.  Headache: The Journal of Head and Face Pain, 51(6): 1029–1045.