Hi @dmmacvicar, welcome to the forum 
Depth sensors need to be implemented as AP_Baro libraries in the ArduPilot firmware repository. I don’t believe any of the existing ones use an analog reading, but flight controllers often have at least one available analog to digital converter (ADC), so it should be possible to create a driver for your sensor that uses the hardware abstraction layer (HAL) to access an ADC.
Note that if you’re wanting to use it on an underwater vehicle you’ll need to set it as a water barometer.