It is not possible to program the ESP32 on the Argon.
Well, OK, it is possible, but it’s not recommended.
The ESP32 firmware is referred to as NCP (network co-processor) and it is possible to flash it OTA or in --serial mode.
The Argon uses the ESP32 AT command processor mode. In theory you could add your code into this build, build it with the ESP32 build tools, wrap the image in the wrapper needed to be flashed as a Particle binary, then flash it to your device.
This is undocumented and unsupported, so for all practical purposes, the answer is no.