I found a solution that provides the following on the supply side of AirLoopHVAC:

1. hot gas reheat for dehumidification
2. variable airflow
3. primary DX heating and cooling coils
4. an additional supplementary heating coil

I achieved this by doing the following:

Created AirLoopHVAC:UnitarySystem with: - DX Heating Coil - DX Cooling Coil - Coil:Heating:Desuperheater for hot gas reheat - control type is "SetPoint" - if control type is "Load" fans do not operate at variable air volume

Added a Coil:Heating:Fuel to the outlet node of the AirLoopHVAC:UnitarySystem. The Coil:Heating:Fuel is also setpoint controlled.