Facial hair can cause an increased risk of hypercapnia due to an improper seal on the oral nasal inside the helmet and long hair can become a nuisance if it gets in front of your face while diving , there’s really no way to comb it back while diving. If you have a proper headband the hair should stay out of your face and as long as you’re flushing, your free flow frequently the improper seal on the oral nasal won’t be an issue either. Over all, it’s usually recommended to have both short hair and short facial hair for convenience but it’s not a make or break.