I work in a public high school in Korea, I have long hair, it's just over shoulder length. When teaching I ALWAYS tie it back, into like a bun, don't know exactly what it's called but it's shorter than a ponytail. I have had several jobs in several countries in Asia and so far had no problems. For me it is is the kind of thing where if you are a bad teacher then they will find something about you to complain about, for example a pony tail. If you work hard and do a good job then it's not a problem, in fact most of my employer have come to like it. I also have a full beard, again I've never had a problem. Work hard, teach well and that kind of thing will be overlooked.