I would define sex work as the exchange of money for the sexual use of a person's body, whether that use involves direct contact or voyeurism. By this definition, fetish workers and dommes are sex workers, strippers are sex workers, prostitutes and people working out of massage parlours are sex workers, nude/porn/fetish models are sex workers, as are professional porn actors.
There are a lot of strippers and models who hate to be thought of as sex workers. These people often try to tell themselves that lack of certain types of physical contact or penetration, or what have you, makes them somehow immune to whatever they dislike about the population of sex workers at large. This is intellectually dishonest.
There are a lot of neo-burlesque performance artists who identify as sex workers despite the fact that they tend to work largely for audiences who are paying them for the art and dance aspects rather than for sexual stimulation. This is intellectually dishonest as well.