Provide opAmp supply voltage using charge pump
For that particular application you can use a single-supply op amp that can reach ground on its output (given that you have 5V available you might not even need a rail-to-rail). In some cases you would probably have to add some protection (e.g., a resistor) to avoid damaging the input of your 3.3V-powered ADC, however. This means that you don't need to generate a negative voltage, which means you don't need the charge pump.

But to answer your question, as long as you satisfy the supply requirements of the op-amp it will be ok (6V > 2.7V min of the AD8027). These have enough power-supply rejection ratio (PSRR) to be relatively immune to supply variations. But in your particular application, and given that you are using a rail-to-rail op amp, the 3.1V positive supply will be the maximum voltage that you will be able to produce.