There is the argument that the Others possibly have the ability to observe the survivors of Flight 815, not through the video surveillance system, but through telepathy. This is based on evidence that the Others know a lot about the survivors (such as their names, as well as the fact that Tom knew they had 'opened a door' i.e. entered the Swan hatch). This is perhaps because Michael communicated to 'Walt' on the Swan computer and this may have in fact been the Others.
The "Monster" is actually a remote viewing system that can record images that lead back to a system or DHARMA station.
The polar bears, though also existing as "real" on the Island, may also be conjured up after Walt's reading of the comic book.