@MWolf: To directly answer your question:
“Does inviting a person who is known to be harassing to be a speaker on campus, also constitute harassment ?”
Not in this case as the group or person inviting the speaker to campus do not control the speaker’s words or actions, but do specify the topic. Also, this is not a conspiracy to incite a riot or to cause direct harm to another.
While topics can be disturbing to listeners, an important part of education is to challenge individuals to think & analyze beyond their comfort zone. And, as I alluded to in my post above, speaking on controversial topics which affect specific groups of individuals or specific beliefs can have a unifying effect.