The answer is yes, closed cell foam can be glued together at butt joints. I would use foam to foam glue because the set-up time for the glue is only a few seconds instead of waiting for contact adhesive to dry. As far as telegraphing through the fabric, you need to sand the joints flat and then cover the entire area by using contact adhesive and gluing something else that is stretchable, very thin, and can be applied in one piece. While covering the entire area would be ideal, covering the butt joints by themselves with maybe an 8" wide piece may do the trick. This could be something like muslin or Versare. This should be enough to keep the joints from telegraphing through. Why not try doing a separate piece outside the car and see if this works for you. It's also possible that if you sand the joint well enough, the joint won't telegraph through without doing anything. Again, try it outside the car to see what works. I think you have a better chance of it not showing through because it is a concave surface rather than convex.
No one lives forever, the trick is creating something that will.