Op-amp driving mosfet changes hystheresis thresholds?
The only connection R8 makes to the MAX9015 is on the output. R8 is 100 kohm therefore it will have virtually no effect on hysteresis levels. Even if R8 terminated to ground it would only load the MAX9015 output extremely lightly.

If you look at graphs in the data sheet they show how the peak output voltage can be reduced by load current. At a load current of 1 mA, the output voltage (high) might be Vcc - 50 mV and the low output might be about the same. With a load of 100 kohm your output current might be as high as 50 uA so expect that the error induced in the output might only be 2 or 3 milli volts.

See page 6 of DS.