You can usually force plywood to lie flat on straight frame faces, though it depends on how much torture you need to apply and the hull shapes. For example Eric mentioned it looks easier than the Atkins Marcia, but if you look at the Marcia, it's not a truly developed design, actually intended to have been batten seam, but the sections align favorably enough to permit torturing in plywood.
The frames (for Eric) are made up of pieces, called futtocks.
When the planking is developed and there's a bit of twist, the face of the frame pieces (the futtocks) have a belly in them, instead of a straight line.
As you can see on these two hard chine frames, instead of the sides and bottom being simply straight lines, there's enough twist in the planking that the plywood will cup a little, as the edges are forced into alignment. It's the tension and stress concentrations along the edges that cause this cupping.
On most of these style of designs intended for plywood, I'd skip the majority of the frames entirely and tape or batten the seams. It makes for a lighter boat and cleans up the interior quite a bit too. I'm not sure why Spira (and others) insist on all those frames on such a simple set of shapes, but some feel more comfort with them, knowing the "boat bit" count rises dramatically.
As to your pounding concerns, well you can mitigate this to a degree with the design, but all flat bottoms will find a set of sea state conditions, that will just toss lots of wetness and pound. This can often be eased with a speed reduction and or modest course change.
