There's no way Facebook would allow someone to use Facebook Dating while their relationship status is set to "married" or "in a relationship." That leaves only alternate accounts as an option for someone using their dating to cheat, but I dont think Facebook has much of an alternate account culture.

Unless someone has an account for personal use and an account for "work" use that they cheat with? And their work friends list are all part of the pool for the Facebook dating protocol? That would get real messy.