Since the current is so low you could skip the diodes (which would have to be configured for each system) and put a small micropower LDO linear regulator in there. Then it would be a universal solution.
You may need to put a current limit resistors on the I/O line(s) as well, I have no idea what the output impedance of the servo signal line is, but if it can source more than 1ma of current it may fry the I/O line because the voltage will be over the MCU's VCC from the diode or the regulator.