i mean if you are going to the lengths of using a proving unit to show your safe working practices id say the correct testing equipment more important than the proving unit.
As far as im aware (and i could well be wrong) a 1553 is not suitable for this, a matindale voltage indicator or a test lamp is. i cant see how a 1553 is gs38 complient as this would require fused test leads, fused test leads have a impact on your readings when live testing, there is a document out there produced by megger detailing the pit falls of fused test leads and its equipment.
This is all irrelavent anyway, i have never been asked anything like this on a assessment, if i was i would be using my martindale voltage indicator and the incoming supply to prove dead.