I guess tickling videos are considered a form of "porn,"
Yes, it's porn. It will be distributed on porn websites. The producer you work with has to file paperwork complying with laws regarding porn in your country. Even if you keep your clothes on, it's still considered porn by law in most places.
I assume universities would fire a professor if they found out they were in "porn"?
It's definitely a risk, yes. Here in the US, if you were a schoolteacher you'd be fired in an instant. Professors tend to be harder to get rid of, but it's far from impossible.
Your options are to either appear in a video and risk being fired, or conceal your identity using a mask or blurring/pixelization and a stage name. A stage name is a must either way, actually, because all it takes is one nut with an unhealthy fixation to hunt you down, and this community is
loaded with them. You don't really have any other options.
Yes, the models that have day jobs either work in fields where nobody would care what they did on the side, or they conceal their identities. Others do modeling full-time and either don't care if someone "outs" them, or they keep a separate persona for fetish work. The risk is still there (some of those people I mentioned before can recite you every alias their favorite models have worked under at the drop of a hat), but it's lessened a bit because it's not uncommon for "regular" models to do fetish work and few agencies/photographers (the people who pay a model's salary) care.
Most of the "day job" girls I work with are either students (no job/part-timer) or pushing papers in an office somewhere. Not exactly the kind of front-facing position that an employer would feel impacts the company negatively if someone outed them to their boss. You, on the other hand, would be.