I don't know how (or why) Moonshrimp includes flour in their beer. It's hard to imagine that an unroasted, unmalted GF grain is going to contribute much in the way of flavor, in flour form or otherwise. Corn and wild rice do offer some flavor, but rice, quinoa, millet, buckwheat, and amaranth do not seem to contribute much in the way of flavor unless used exclusively, in my experience.
I would not imagine a nylon sack will do much in filtering out the flour, either. I'm curious why you would consider trying it, i.e. what you would hope to get out of it.