Yes, the MAX30003 can be used for 3-lead electrode ECG recording. The third lead can be connected through VCM and is used as a common reference to the differential signal between ECGN and ECGP. For an example of this, see the schematic of the MAX30003WING development board.
MAX30003WING Evaluation Board | Analog Devices
MAX30003WING Evaluation Board | Analog Devices
