I have never heard of this check. It does make sense.It is up to YOU, to try to inhale from the regulator BEFORE it is pressurized and ensure that the integrity of the second stage is in tact and there are no (or negligible) leaks when you suck a gentle vacuum.
I wonder if many people actually do the vacuum test before diving, I generally do it every time I load the regulators into the gear bag (the night before) and sometimes do it on the boat- but it should be done every time before a dive - even on brand new regulators.
Can anyone think of a reason not to add it to their pre-dive ritual? It would be easy enough to do just before you turn on the air to perform the other checks.