Although a c-2c ladder n/w can work as a voltage divider; I don't think it can be used as a DAC. b/c once the capacitors charge up with a particular voltage, you will have to provide a discharge path (using resistors), before they can be used for a new input value.
Even if you do provide the resistors for the discharge path, the RC time constant will limit the response of the circuit.
Finally, its usually difficult and costly to fabricate capacitors in ICs, whereas resistors can be easily implemented using o/p impedance of current sources.