Whenever repeat signs are to be observed, the instructions for this will be written at the very bottom of the first page of the piece of music you are preparing. See below for an example.
Da Capo & Dal Segno Signs
The general motivation behind guidelines such as ignoring repeat signs is essentially to save time during examinations. By saving time, RCM is also probably able to accommodate more students on a given day. Also, repeating a musical passage can be seen as superfluous on an exam since the examiner has already heard it once and was able to evaluate it the first time around.
While observing repeat signs may hardly be felt in beginner pieces, it becomes much more noticeable with higher RCM Levels, where pieces themselves get longer and more difficult, therefore extending your exam time quite a bit. So do your best to follow the RCM guidelines as much as possible!