That's a shame.
People take rivalry way too far. Its supposed to be in the spririt of competition in a good way, not as the evil enemy.
Heck its not even a rivalry anymore. Plymouth is gone. Dodge is largerly about trucks. Likewise Pontiac Oldsmobile etc.
Tell you what. John Heinricy, GM's director of performance, had no problem driving a Dodge Viper to prove they were as capable of wins as the Pheonix prepped Corvettes he was normally driving.
Lemme find some documentation. Maybe it will thaw the ice.
http://heinrocket.com/press-2010-09-21-Road-America.php