H'okay, from the Roget's thesaurus, which I only just thought to look up, "Invigilator" is AN ACTUAL WORD! Hooray! It is similar in meaning to "keeper".
Now my sister who sat the HSC 2 years ago told me "They're called EXAM SUPERVISORS, IDIOT, HOW HARD CAN THAT BE!?!?", so that's what you call...