jhine, the Watchtower has never taught that any of the extant manuscripts of the Christian Greek scriptures contain the tetragrammaton. But none of the Christian Greek scriptures go back to the first hundred years which is why this fragment of Mark is of interest. However, there are parts of the Old Testament translated into Greek which still contain the tetragrammaton and that is one of the reasons Jehovah's Witnesses maintain it was likely in New Testament manuscripts about the same time.
It does seem in some manuscripts that it was written to bring attention to the name, possibly to warn the reader about pronouncing it. But in others the name is written in Greek as iaw (yahu) which gives no such indication. Further, even in those cases where it may be written to alert the reader, one needs to bear in mind the many different strains of belief in first century Judaism and whether the early Christians would have been bound by the traditions of the Pharisees and priestly class.