Can you use an Arduino to control the output current and voltage of a DC/DC converter?
Yes, and it's actually far simpler than most realize. I've tried digitpots, but they are quite un-linear and only handle 5v, unless you spend $$$. Early on, i had soldered an LDR in parallel to a buck converter's adjustment pot, and fed that PWM. It worked to somewhat adjust the vout, but had a lot of ripple and was not linear. I had gotten an MCU-controlled linear PSU going, that wasn't too hard, but i always wanted a buck. Just recently, i've found an awesome method and built several MCU-controlled SMPSs.  You don't have to have any special parts or de-solder anything!

Basically, you:


use a buck/boost (or dual) with a built-in V-adj potentiometer. 
use a lowpass to convert the MCU's PWM output into a 0-vcc signal. 
feed smoothed PWM voltage to a unity gain opamp to buffer available current. 
create a common ground between MCU and SMPS.
feed the buffered 0-vcc control through a resistor into the pot's wiper, ~200-1k.
the amount of "injected" voltage will be inversely proportional to the SMPS's output voltage.


Since most SMPS's feedback is in the area of 1-2.5v, the 0-3.3/5v output of the MCU works well to provide or take away feedback from the regulator. The best part about this scheme is that output voltage regulation is maintained by the SMPS's hardware, the MCU just sets an offest. In short, you can set it to 10v via the MCU, attach a big load, and the voltage stays at 10v!

I've used this technique on the xl4005 and the xl4015, but i would imagine it would work for just about any common driver package.