Does a vivisectionist benefit from a healer’s kit bonus?

The vivisectionist’s cruel anatomist ability allows him to “use his Knowledge (nature) skill bonus in place of his Heal skill bonus”. Does this mean that using this ability while making a check ignores the +2 circumstance bonus from a healer’s kit? If so, would the kit would still be required if one wanted to avoid the -4 penalty to treat deadly wounds?