Dr C,You are about to enter that place known to DMs as the Place of Sincere Regret.
I would refer you to page 35 of Exalted Deeds. The ability damage done by ravages affects undead and evil elementals unlike normal poisons. A Fortitude save is implied but, to the best of my knowledge, not explicitly stated.
As ability damage, multiple attacks do indeed stack just as any other form of damage stacks whether from repeated blows (hit point damage) or additional doses of poison (ability damage) etc...; it is not a penalty.
In addition to the listed damage, page 35 states that the ravage does ADDITIONAL ability damage based on the Charisma bonus of the victim. Yes, the higher a creature's Charisma, the MORE ability damage it takes.
Personally, I would immediately discuss with the player that you will not be allowing the additional damage based on the victim's Charisma score as this is just a piece of Erroneous Design (BoED: Book of Erroneous Design). This is far too powerful for a feat particularly when it can be gained as bonus feat.
I would also insist on using the listed DC (14) and not the normal formula for poison of half the character's level or hit dice plus Con bonus. And then fudge every saving throw for any opponents that the character tries to infect with "holy urine".
The rest of the VoP works out OK in actual play but this feat is just bad, bad, bad design.
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