It is possible to use a DAC to provide a voltage to the MAX16818 so that the current from the LED currents is regulated. One limiting factor is the common mode range of the current-sense amplifier CA inside the MAX16818 which is 5.5V. There will also be a limit on how fast you can change the LED current via the current-sense amplifier. You will have to make sure that your DAC output has a very low impedance and that the output impedance is not a function of the digital code. In any case, a buffer can be used in order to interface with the CSP pin.