The MAX31865 simply converts the ratio of the differential resistance across RTDIN+ and RTDIN- to the reference resistance and outputs this ratio in digital format to be converted to a temperature reading. So yes, it will work for any RTD sensor such as an Ni-120. You will just have to model the resistance to temperature conversion for nickel instead of platinum.
However, the MAX31865 was designed and tested with a Platinum RTD in mind so the testing results referring to the ADC accuracy stated in the datasheet will be different when using a Nickel RTD, and the rule for using a reference resistance equal to 4 times the resistance at 0 degrees Celsius will also not apply. Instead you must choose one that will cover the entire temperature range you plan to measure.