You are wise to be concerned about food safety. And you are right about the significance of specific ingredients in determining what steps are needed to keep a food safe.

In the case of marinating a soft cheese, the key to keeping the product safe is more about refrigeration than it is about the strength or quantity of the acid in the marinade. Mozzarella balls in oil, vinegar and herbs can be safely held in the refrigerator for several days at 40 degrees Fahrenheit or colder (recommended refrigerator temperatures).

The concern with botulism in oil/herb mixtures is heightened when that mixture is stored in a jar or decorative bottle at room temperature, as it often is.

As a review, here are a couple websites about marinating in general and marinating meat. The general principles apply to any food.
http://www.foodsafety.gov/blog/marinades.html
http://extension.usu.edu/files/publications/publication/FN_FoodSafety_2009-01pr.pdf

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