I have a circuit that requires six 18-bit DACs (AD5680) on it. Each DAC draws ~800µA at the high voltage output +5V and ~400µA at 0V output. Is there any issue with a single REF195 voltage reference for all of the DACs? The AD5680 is rated to supply 30mA. It can be assumed that the DACs are "close enough" to the voltage reference to not be an issue. The DAC output can be considered static, the output will change but not dynamically and there is plenty of settling time. I'm concerned with noise on the voltage reference supply bus or power supply pull or some effect that I have not considered.
You're probably okay using a single reference, but you may well be able see a bit of crosstalk between channels.
Keep in mind that the reference input is not differential so any difference in ground potential (say due to current from the DAC output) will show up as a slightly different DAC output voltage (measured with respect to the local ground). With a 5V Vref, one LSB is less than 20uV. A 300 mil trace 500 mils long (1 oz copper) has a resistance of about 0.8m\$\Omega\$, so about 20mA will cause a 1 lsb shift in full scale.
Not too bad, things get much worse when you're trying for 24+ bits.