Raising Op Amp Supply Voltage Without Affecting Output Voltage
My understanding is that the supply voltage just dictates the ceiling of the output voltage. 


Yes, that is correct.

Yes, but it is also the problem.

The danger is that in a power-up, fault, or sensor disconnection or short that the op-amp output will exceed the maximum allowable input voltage for the ADC. This limit is likely to be 5 V or very slightly over. Exceeding this will destroy the ADC chip.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Over-voltage protection.

To do what you require some form of over-voltage clamp is required. This could be a resistor and 5.1 V Zener (Fig. 1a) or resistor and diode to +5 V (Fig. 1b).