I don't know I thought all digital servos used a pwm.
At the input, absolutely. The tricky part that is not completely understood for the servo you have though, is how it controls the motor directly.
Remember that because your cracking this thing apart, you have your original input signal to the servo control board and the output to the original motor to look at. It's the control board's method of controlling the motor itself that we are looking at.
We could operate on the assumption that in it's:
neutral state the motorA and motorB wires are at 2.5V.
forward state the motorA wire is a higher voltage than motorB wire
reverse state the motorA wire is a lower voltage than motorB wire.
but the scary word assume makes an ass-u-me..
This is the logic we need to convert to send to an H-bridge. The diagram you posted has it's flaws. It may work well enough, but there is concern of the longevity of the mosfets. Instead of looking at the diagram, making assumptions and correction the mistake. It seems as though Kris has put some thought into a better solution which I loosely follow, but not enough to finish up.