At VUW, the statute on conduct includes an item on "misconduct in research" which covers this topic. In particular, it refers to the guidelines established by the University's Human Ethics Committee (HEC). (Here's a link to the calendar entry.)
The guidelines are available from the secretary of the committee (currently Linda Bowden) and are about 30 pages long. They state:
Whether they are teachers or students, all members of the University whose teaching or research involves human subjects or human tissue or otherwise affects people's privacy, rights, and freedoms, should always consider whether their work requires ethical approval in accordance with these guidelines.
The guidelines suggest, and I later confirmed, that much usability testing does indeed require approval. This normally involves reading the guidelines and submitting an explicit proposal that conforms to the guidelines.
Here are files with the forms for an application: