"How would something like that work when snapping the vertices to the grid will create non-planar vertices?"
Having trouble understanding what you mean PB, surely not snapping them to the grid would create non-planar faces.
This issue is plaguing me in hammer right now. By rotating objects, or flipping them, it's making the vertices go onto a microgrid, out of the normal grid. and this is creating weird artifacts everything and it's annoying as hell - especially when it was originally on grid.
It's merely a point of using a round function on every vertex. If it's stored as a plane or face in a VMF, surely some mathematical jiggery pokery could be used.
this sort of crap
it may not be an issue for GS or source to render, but using it as a reference for other objects , or simply surrounding the brush with other brushes , creates an issue