[Al Skierkiewicz]

Aaron,
Any multi-conductor cable has been legal in the past for sensor wiring provided that no power is supplied in the cable. If you are powering sensors, then the appropriate electrical rules for power wiring will apply. Usually #22 or #24 wire would be sufficient.
It is unwise to "common" PWM signals anywhere beyond the DSC. The generated noise and subsequent issues with driving your controllers makes this bad practice. (Look up 'ground loops' for general discussion) The PWM input of a speed controller is opto-isolated and by definition is supplying switched current to drive the isolator. The power supply and board layout of the DSC is designed with that in mind.
As mentioned for pneumatic valve input, multi-conductor cable has also been legal in the past, however, the length of your connection should be considered when choosing conductor size. Significant loss can build across a long, small gauge, cable making valve action unreliable.