So does leading theologian in the Emerging Church and influential evangelical teacher Brian McLaren, really think that God—through Muhammad—founded the idolatrous pagan religion of Islam, which denies the Deity of Christ Jesus?

Decide for yourself; the following is from McLaren’s book Finding Our Way Again:

Christianity, Islam, and Judaism have more in common than many people realize because they all share a primal narrative, and they all flow from a common sacred fountainhead: a single figure, at once famous and mysterious, a Middle Eastern man named Abraham of Ur.

We can date Abraham’s birth to about 2000 BC, in modern-day Iraq, near present-day Nasarif. Like Moses, Jesus, and Muhammad—and like us—Abraham was was raised in a pluralistic, polytheistic world. During his lifetime, he lived side by side with others who honored many different gods and praticed many different religions.

And during his lifetime, Abraham—like Moses, Jesus, and Muhammad—had an encounter with God that distinguished him from his contemporaries and propelled him into a mission, introducing a new way of life that changed the world… How appropriate that the three Abrahamic religions begin with a journey into the unknown.
 (22, 23, emphasis mine) 

See also:

BRIAN MCLAREN ATTACKS THE SUBSTITUTIONARY ATONEMENT

ISLAM AND CHRISTIANITY: THE DEITY OF CHRIST

CHRISTIANITY AND ISLAM—THE SAME GOD?

JESUS OF ISLAM