Just to answer your question, yes, some people can be fired for posing nude.
Teachers are particularly targeted, as there is a morals clause, usually in some fine print, upon hiring for the first time. Usually public schools, don't know about private. It never shows up again when teachers are "renewed" for the subsequent years. The same clause has been used to fire pregnant, but unmarried, teachers.
I suspect certain other businesses also have vague morals clauses. I vaguely remember something when I was a JCP employee. Truth is, a corporation/business/employer should have a right to hire or fire people, but they should also make clear their rules. That is where I think you will find the dilemma - rules and interpretations and how many employees actually bother to read when signing on?
I suggest asking your models to locate a Memorandum of Understanding, or some equivalent, to find out.
good luck... geez, yet ANOTHER thing for you to worry about. Your perseverance is remarkable.
Anybody else have any information about this daunting question?