Because zero names an absence, traditions that value negation have found it useful. In the Kabbalah the highest aspect of the divine is Ein Sof, the Without-End, and beyond even that the mystics place Ayin, Nothing, not a deficiency but a fullness too complete to be a thing, from which the something of creation emerges. Daoist thought gives wu, non-being, as prior to and generative of being, a theme the Tao Te Ching states directly when it makes the useful part of a vessel the empty space inside it. The Buddhist shunyata, from which the numeral takes its Sanskrit name, is not blankness but the absence of independent self-existence in things. None of these systems is doing arithmetic, but each reaches for a figure of productive emptiness, and zero, once it existed, supplied one.
The modern American numerology chart that assigns digits to letters, A to I as one to nine and then repeating, credited by its own successive writers to Balliett in 1908, Cheiro in 1926, Florence Campbell in 1931 and Juno Jordan in 1965, has no letter that answers to zero; the cycle runs one through nine and starts again, so zero never arises as a name-derived core number in that system. It appears only where a birth date already contains it, the tenth or twentieth or thirtieth of a month, and there it simply contributes nothing to the digit sum, a different kind of absence from the missing letter, one built into ordinary arithmetic rather than into the chart's design.