To my knowledge, yes.

On nitro it's not a problem since they have their own power source (as an example), but with electric's IIRC all ESC's supply servo voltage at 6V, not the 7.4V HV servos need.

I have never used a Savox personally (I run KO stuff), but I've seen more than one of my friends go through this and the only solution was getting rid of the HV servo or running a RX battery pack.