had a friend teach there - said it was great in the summer, but terribly boring in the winter
remember it is a fairly small island and while its more tropical than the rest of Korea I doubt you will be sunbathing on the beach in December.
It's not cheap to get from the island to the mainland (by plane) and can be very difficult to get a seat during peak periods (which is when you get your vacation!), so reckon on staying on the island.
all depends on what suits you
And yes, there is a fair number of teaching jobs there.