The temperature sensor on board the MAX30102 is not needed in Maxim's HRM/SpO2 algorithms. The temperature sensor was leftover from an older through-process. It is not an accurate temperature sensor so no, it should not be used to reliably measure body temperature. An external IC sensor should be used for any (skin contact, for example) temperature measurements, but, again, body temperature measurements are not needed for any of Maxim's HRM/SpO2 algorithms.
