That's a little pessimistic - given you filter the output with a smoothing capacitor you can then pass this through a resistor to turn it into a current. However you will need to know the input voltage that the controller uses for its current-sensing input - I couldn't seem to find the full specs.
Have you ever worked with loop powered 4-20ma current loops? I ask because it is industrial standard interfacing method, but is more complex then may first seem, especially for simple interfacing with a Arduino. One requirement is to deal with the 4ma 'live zero' concept. This allows a current loop measurement system to differentiate from a 0% measurement or command value and a broken or open loop connection. So one can't use a PWM output of 0% duty cycle to represent a 0% command to the controller that needs to see 4ma for a valid 0% command. Again 4-20ma current loops are a little more complex then just filtering and driving via a fixed resistor.
Then there is the issue of which side of the current loop is providing the loop current, if it's the motor controller then the Arduino interface needs to simulate a passive dynamic adjustable resistance to the loop. If the controller is expecting the Arduino to power the loop then it needs to supply the loop compliance voltage source, typically a 24vdc potential.
All in all, using the 0-10vdc interface to the controller will be a much simpler interface.