I paddle 0 degree offset in the biggest water I can find (the mighty Slave river
at the moment), and it works totally fine. If you're concerned about that upper blade catching the pile as you punch a hole, worry more about your head and body. I have not ever had that be an issue. Also, the vertical stroke argument is a good one, except it only applies to strokes on the right hand side. Strokes on the left would be harder. 0 degree is the most symmetric possible.
Furthermore, my friend John here, who has only ever paddled the Slave river (plus like two other rivers) is pretty much calling you guys sissies. To punch holes in big water, you don't sit up straight and use the boof stroke you're probably envisioning from small water. You reach deep, and tuck as hard as you can. The offest does not come into play.
So basically, don't listen to anyone who tries to stop you. 0 degree all the way!