would the arduino work to provied PWM and Volts in & out
Sure. A simple implentation would be to use a pin to short the coil to ground periodically - applying pwm to that pin. Lower duty cycle on that pin means higher output voltage.
A more sophisticated version would use the adc or analog comparator to detect the output voltage and based on that, output a pwm signal to ground the coil via a switch - that's effectively what a pwm controller does, in hardware. The difficulty there is the control algorithm.
Many high-end dc/dc converters are build around mcus (by Freescale). So you are onto the right track.