It is a double-edged sword, like everything else on Yelp. But to answer your first question, no, a business cannot opt out. If you are not finding your ex-T, it is probably because nobody has reviewed her. Another thing I learned about Yelp (I had a boss totally obsessed with it) is that 1) you cannot use an alias and 2) until you have reached a certain quantity of reviews they remain hidden on the site, filed under "comments not recommended". Therefore, finding anything regarding potentially sensitive information on the business or the user is very rare.