Does primer really require 3/8 -1/2 inch nap?
They're trying to help you apply it efficiently, perhaps because it is thick.

You can beat roller texture by using the "roll and tip" method.  That means rolling it out to lay it down, and swishing over it with a brush wetted in paint to remove the roller stipple.  I do it so often that I find myself doing it even when I don't need to.  

The link and similar Youtube videos talk about marine paints, the best of which have very good flow-out and will "look sprayed" if roll/tip is done properly.  Disregard what they say about mineral spirits and chemical thinners, thin according to your paint's instructions.