My observation is that using an Arduino to drive servos results in twitching servos. Nothing you would notice while they are in motion, but if they are supposed to stand still, they twitch. Some brands worse than others. I switched to pca9685 and they are rock steady.
What are you using to drive the brushless motors? A standard RC brushless motor controller that takes servo style pwm inputs? Should be as simple as controlling a servo. If so, take a look at this article: