The "J" tubes have a cap on the end, think of them as deadends. All the "J" does is help to tune out the annoying droan, it nothing for the actual exhaust gas itself that still exits the tail pipe tips at the rear bumper.
Even if they were not sealed I don't think it would be much of an issue as not much gas goes into them. Mostly just sound waves. They are only just warm to the touch compaired to the rest of the system.