Does the “Agony Touch” stack with a Ghost’s Draining Touch?

Ghostwalk introduces, among others, a feat called “Agony Touch”. This Special Ability allows the ghost that takes it to deal 1d4 ability damage to a target, to a physical ability chosen at time of taking this feat. However, many ghosts also have the inborn ability “Draining Touch”, which allows a Ghost to drain 1d4 ability points from a single ability score of its target. Does Agony Touch stack with Draining Touch? Or is it merely a way for Ghosts without this ability to gain a weaker version of it through feats?