RE: Using a RotoZip bit in a Dremel for shaping a stack of ribs?
It might work if you have a template to guide the bit; that is a plywood rib at final shape which you can run the Dremel around to shape the ribs.
You'll need a router guide bushing to run against the edge of the template.
What you are attempting is done all the time in full scale builds to get identical parts.