Does atheism = dogmatic materialism? How would Nietzsche feel about this?
No. Not necessarily.
Nietzsche frequently ridiculed dogmatism in all its forms — and the world-views of physicalism and materialism. And he pointed out the origins and functions of dogmatism in the unconscious, historical formations, in power structures, and in abstracted lies.
Further, while Nietzsche disparaged most modern forms of religiosity and many forms of theism, Nietzsche himself was not necessarily an atheist. A god has to exist first before the we who kill it kills it. (Not to mention what God’s deathmeans to Nietzsche!)
I believe (and I’ll write a more thoroughly on this someday) that the entire project of Nietzsche’s philosophy, was precisely this: the smashing of dogmatism in all its forms — especially the residual slave-moralities that persist after a particular dogmatism has been supposedly destroyed. We see this with the rise of dogmatic science after and with the Enlightenment — the destruction of the old aristocracy and new universal suffrage — modern free market economies creating effectively new aristocracies without the need to call on Divine Investiture — modern medicine, especially modern psychiatry, and prison systems taking the role of the Christian confessor and enforcing Christian penance.