Where does the current in a Dickson Charge Pump come from? Does the oscillator/PWM pin of a microcontroller also source current?
It will come from both sources.  I would suggest building a discrete CMOS inverter with a power N-channel and P-channel MOSFET transistor, and then driving this with the PWM signal from the microcontroller.  This will alleviate the I/O pin from supplying power.