The one time i got this question it was not about souls, nobody wants a philosophic/religious discussion at this point. They just wanted to know the number of persons (which excluded both AVIs).
And ATC was perfectly satisfied with the answer in time for the fuel remaining, which was important for their planning purposes. But i later asked myself if the fire services would find it rather more helpful if the answers was in another unit, the only we have indicated on board is Kilos.