Your examiner should make it clear beforehand when/if he will accept use of VOR. If he does not mention it, then ask. I assume we are talking PPL Skill Test here.
Usually, suspected sly/naughty use of the VOR (or ADF, RNAV etc) is easily dealt with by deselection of the frequency by the examiner ! In my view, there is nothing wrong with monitoring position / progress by VOR on a practice diversion but I suggest you check this out in advance with the examiner.
Just make sure that if something is used it is used properly !