If there was no interference in the first place, coiling/wrapping is unlikely to introduce any. Adding ferrite bits is overkill, unwanted extra weight in a small model, and costs a lot more than a tie-wrap. They might have a use on motor leads, but distorting a sharp-edged signal in the servo leads is unlikely to do any favours. If it was extended servo leads, that would be a different story altogether, but only if interference was being picked up.