As long as it contains ANYTHING that could (and does) have a harmful effect on a subgroup of people, it is not a placebo, and no amount of twisting the truth will make it one. Saying that "it functions as a placebo" does not minimize the harmful effects; it just confuses people into believing so.
No. The definition of a placebo is "a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient." (that's from wikipedia at least).
So it has to be something that the person thinks is medicine (or prevention) for the disease, but actually isn't. Research ethics would say it should also be something which the researcher believe is not harmful based on the best available evidence, but that has nothing to do with it being called a placebo.
A placebo is something which has no positive medical effects, and anyone who thinks otherwise just has a misconception.