How do you cut threads in plastic coated steel pipe?
I spent hundreds of hours on a Rigid pipe threading machine and used the same dies for black iron, galvanized, and green coated iron gas pipe. The only issue was the green coated pipe is slightly larger on the O.D. (due only to the coating) so is a bit difficult to get the threads started. With the machine, I could grind a bit of the coating off by levering the dies open a bit, to get the thread started. With hand dies you may have to use a different method to scrape a bit of the coating off the end of the pipe, maybe just use a sharp knife or a file. Once the dies bite they will grind right through the coating, no clogging. 

The official response will still be "follow the manufacturer's instructions", but I think you will be fine.