Mr Hat,
Kind of. What it (CAR256) says is:
(2) A person acting as a member of the operating crew of an aircraft, or
carried in the aircraft to act as a member of the operating crew, shall
not, while so acting or carried, be in a state in which, by reason of his
or her having consumed, used, or absorbed any alcoholic liquor, drug,
pharmaceutical or medicinal preparation or other substance, his or her
capacity so to act is impaired.
Which is essentially, as you say, the same as "under the influence". It is not clearly defined by a certain level of the drug/alcohol and they would need to show that you were actually impaired at the time.
Its like riding a bike when you're pissed. They can't do you for being over .05 but can nail you for DUI so long as you are clearly impaired (and you don't necessarily need to be over 0.05 either!).
Yep, I just looked that up, because I am on non-drowsy flu medication, with which I have done a ground trial to assure it does not make me drowsy, and I am flying tonight.