Seems a bit pessimistic! The AM882 claims to have TTL-compatible opto-isolated inputs, which sounds fine to drive with the ATmega chip on the Arduino board. Why put something else in between, unless it happens to make connections easier? Assuming it's a Uno board with a plugin cpu, worst that's likely to happen (and even then only as a result of a fairly significant fault elsewhere) is making the ATmega chip go pop. A 328P costs about £3, which is less than a typical breakout board!

The idea of cheap hardware plus open-source software giving better-than-PC performance for a fraction of the price of the cheapest motion controller is very attractive, and I would like to follow this one and hear how it goes.