Well, the answer is "yes and no". Let us explain to you how it works! Used quite often for emerald enhancements, cedarwood oil discharges very quickly. Be careful though, as when exposed to ultraviolet light, this oil emits oxygen as a by-product and can darken the stone with stains. In most cases, cedarwood can be a good way to help you with fracture-filling in emerald, because it is colourless and has a refractive index close to emerald. Remember that every couple of years, you'll need to reuse this stone treatment as the oil will wear off after a while.
You also have to keep in mind that not all cedarwood oil is going to do the job! Be sure you use high-viscosity (scientific grade) cedarwood oil for emerald enhancement, not cedarwood oil used for perfumes, massages or wood care.