hey
I am that guy you saw doing it for an ESC 
With the very same hardware and firmware which you saw me using, you also can drive a servo, actually up to 4(6) servos with a board.
In general, in order to connect a servo which uses PWM to the CAN bus you need a piece of electronics which translates between the CAN bus and outputs the PWM signal for the servo. It’s kind of a converter if you like, CAN on one side, PWM on the other side.
I did create such a piece of electronics, hardware and firmware, and that’s how I managed to do it with the ESC’s.
Hope that clarifies things a bit.
Cheers
Olli
