This is the crux of the main problem with zero tolerance stances. That "in any form" gets interpreted in the widest possible way possible beyond the point of absurdity. This is because it is an absolute stance in a realm which is inherently subjective and relative to the various points of view involved.
> "when corroborated"
I think this helps with this a bit, as it requires at least one (hopefully more) other subjective view on whether it was harassment or not. Hopefully it will be enough.