The PPM encoder allows to encode up to 8 PWM (pulse width modulated) signals into one PPM (pulse position modulation) signal.
http://ardupilot.org/copter/docs/common-ppm-encoder.html you need it to transform the PWM output to something that the controller can recognize.
If we are talking about the frame, yes, you can. But the ESC has to be a Symonk (firmware).
With ardupilot you can do that, just compiling what you need.
Our shields are supported to work with ROS, you can use it for rpi zero and rpi 3b. Actually for the 3b+ is not working that well.