[Al Skierkiewicz]

philso,
None of the controllers that I have looked at have a raw opto-coupler input connected to the PWM port. There should be a series current limiting resistor so the V forward difference should not show up as a problem. That being said, single point of failure is likely to raise it's ugly head if one is not careful. A bad controller will take down all three, a pinched wire will take down all three. Your mileage will vary.