If we get a definitive ruling on this chimney question, it should be known as the Santa Clause. Ho ho ho.
My immeditate response is, yes the OC should pay for the chimney being swept (unless somethere on the strata plan it says it's not common property). But you should have got approval first so you may end up paying – unless you can show it was a genuine emergency (like a fire risk). Making sure Santa can get down the chimney is probably not an emergency (well, not for a couple of weeks, anyway.)
JimmyT