Yes. If you use different servo types for eCCPM, then the swashplate will not move evenly up and down with throttle movement. This will cause unwanted cyclic/collective pitch interaction and make hovering difficult.
The Phoenix series governor mode functions the same as standard governor mode, but the RPM is selected by a different method.
Here is the explanation of the Phoenix governor mode, directly from Patrick del Castillo, the designer of the Phoenix ESCs: