These two diodes protect the output pin from external over- or under-voltages ..
As you can see one diode is connected between pin and Vcc, it claps voltages at Vcc+0.5V (depending on the Vf of the diode), the second diode is connected between pin and GND, it claps voltages at GND-0.5V = -0.5V ..
If the output is not exposed to voltages beyond GND(-0.5) and Vcc(+0.5) it’s possible that they will never act as protection .. they will be just sitting there doing nothing ..
And one more thing, if the IC pin can not tolerate voltages above Vcc+0.5V and Vdd-0.5V these protective diodes have to be of Schottky type, as for standard silicone diodes the forward voltage is roughly 0.7V ..
Rgds,
IanP