Yes, according to the The Bread Baker's Apprentice, although I doubt it has a lot of diastatic power.Probably for most, but if you do long rises or use pre-ferments, enzymes play a big role in flavor. It basically a slow motion mash.
Bread flour (King Arthur at least) contains some malted barley flour in it to convert some starches into sugars during the rise. I don't know if there are enough enzymes to do significant conversion, but maybe.
I thought it was only for flavor.
But is the flour diastatic? Does it actually have enzymes?