I just confirmed my interview date on campus. Interviewing beginning of December, super late but it was the only time that works with my schedule.
In terms of off/on, I had the same question. I spoke with some people and I got mixed reviews. I think if the burden of traveling to Chicago is not great, it is worth while especially if you have not yet visited the campus. If you have seen the campus and/or its extremely burdensome to get there, I would go with the alumni interviewer.
I do not think it can be a hindrance since they will not let Chicago based applicants interview on campus.