INL and DNL are DC characteristics both for DAC and ADC. They are measured at low speed, when everything in the DAC has settled.
Sampling rate of the dac is defined by the rate at which your input date comes in. DAC by itself does not sample, it receives samples from whatever digital is driving it. Speed is usually something related to the minimum time required for the DAC output to settle to within the required precision. So, DA has to settle for the time between two input samples.