The output current would be summed against the
output voltage through a feedback resistor, to get
a voltage DAC output in the end. That makes a "virtual
ground" (or common mode voltage) which you would
be best off making match what you see in test figures
for the linearity / error parameters. On older +/-15V
parts this is commonly ground potential but single-
supply systems will have a VCM chosen instead. If
output current is unidirectional then another resistor
from a reference voltage may be used to provide
the offset, summed into the same node as the DAC
current.