This depends entirely on what boundaries you have set in your relationship(s), and whether the person who is doing the sex work is open about it with the other partner(s)
Example 1:
Relationship is established as monogamous, person is open about performing sex work and is not doing things behind their partner’s back/trying to hide it, and both parties are satisfied that it falls within the boundaries they’ve set in their relationship - not cheating!
Example 2:
Relationship is established as polyamorous, people involved have several partners and metamours. Person doing the sex work is not open with one or more of their partners about it, tries to hide it or do it behind people’s backs, or does so despite it being outside of the boundaries set with one or more of their partners - cheating!
As with the vast majority of things in this vein, it’s all about the individuals involved.
This depends entirely on what boundaries you have set in your relationship(s), and whether the person who is doing the sex work is open about it with the other partner(s)
Example 1: Relationship is established as monogamous, person is open about performing sex work and is not doing things behind their partner’s back/trying to hide it, and both parties are satisfied that it falls within the boundaries they’ve set in their relationship - not cheating!
Example 2: Relationship is established as polyamorous, people involved have several partners and metamours. Person doing the sex work is not open with one or more of their partners about it, tries to hide it or do it behind people’s backs, or does so despite it being outside of the boundaries set with one or more of their partners - cheating!
As with the vast majority of things in this vein, it’s all about the individuals involved.