It does not matter if the alleged harasser works for the employer or not; if the former is associated with the university (committee work, etc...) the latter has a duty to respond.
In Matteson v Presbytery of Prince Edward Island a female Minister endured three years of gender-based remarks from congregation members decrying the existence of female ministers. She also received anonymous letters accusing her of sexual improprieties; more specifically of having sexual relationships with other females, including choir girls. She also endured stalking by the chair of the manse committee.
Not only did the committee refuse to investigate the accusatory letters, it also refused to stop the chair of that very committee when he began stalking the minister. The minister was forced to wait two years for the Church to strike a commission to investigate stalking by the chair of the manse committee and another three years for action to be taken to stop the stalking. The commission found that the Minister was innocent of the sexual predation charges, but recommended that she leave the province and get psychological counselling. Soon thereafter, the Church began sending investigators to evaluate the minister; she was eventually dismissed, her pastoral ties severed and her license suspended. In despair, she filed a complaint to the Church. When the Church did not respond, the minister went to the Human Rights Commission.
A Human Rights Commission found the Church responsible for sex discrimination against the minister, including the stalking; even if the stalker was not an employee, he was a member of the Church and served on the manse committee; members of the Church administration knew of his actions and could have acted earlier to stop it.