Why I gave our ADC-T2000 the boot!

The ADC-T2000 is indeed compatible with Dual Fuel systems per ADC.

For a Heat Pump with a fossil fuel furnace auxiliary you would use a “Heat Pump” HVAC type, with a “Fossil” heat type in settings.

Wiring is typically one-for-one with prior tstat.

The only incompatibility would come from proprietary non-standard communication between HVAC and tstat. This is uncommon.