Never heard of that. I went VLC actually in order to pass a test (and I did) so while I'm not positive I was in ketosis (didn't test myself) I would assume I was at least close to it after two weeks of minimal carb intake.
I wouldn't suggest raising ANY suspicion around drug test time, so keep your mouth shut. If you don't partake in marijuana you will be just fine. If you do partake then stop, but definitely "carb up" prior to your test and don't do anything to mobilize fat (don't exercise for at least two days prior). THC gets stored in fat cells, ketosis uses them up but also makes impurities in your fat available in blood and urine, so you'd test dirty as hell (aka positive) for THC if you smoke AND are actively in ketosis when you test.
So, to recap, if you don't smoke, you have nothing to worry about but it wouldn't hurt to up your carbs a bit two days prior to the test if you're truly worried about a false positive, you should be able to slip back into ketosis easily. If you do smoke, don't go into the test in ketosis. Good luck.