First off, does the auto kill thing work on a T6 model? arent most chariots like T3 or something? I dont have a current rulebook to clarify this.
Regardless im quite certain you always get ward and regeneration saves unless otherwise noted.
For instance, a bolt thrower ignores the armor of bloodknights. However if you were to take The Flag of Bloodkeep, they would then get a 4+ wardsave vs ranged attacks of ANY kind including war machines, templates and magic missles.