Is Kundalini Yoga a Religion?

No, Kundalini Yoga (and yoga in general) is not a religion.  It is a technology for health and consciousness that predates religion. It is practiced by people of all faiths and Kundalini yoga teachers represent many paths including Christian, Buddhist, Jewish, Sikh, and others. Yogi Bhajan's background was in Sikhism and he was influential in originally presenting Kundalini yoga in conjunction with the path of Sikh Dharma.  As currently taught, Kundalini teachers can be recognized by the use of white clothes and head covers - often turbans - which, aside from outward religious appearance and personal beliefs, are practical yogic techniques for enhancing the aura and containing energy.