That analogy is bogus. If you can’t disprove a statement without using analogy, you don’t understand the subjects properly.
He paid her for the role of a girlfriend, which is a role that specifically is a ‘lover’ role(ACT LIKE A LOVER), whether or not he sees her as his dead wife does not matter as he never forced any action upon her. Again, your analogy assumes the dentist will be made to do the work of a nail technician, when this situation has nothing whatsoever forced upon anyone.
TLDR; The role she fulfills is that of a GF, even if he sees her as his dead wife, she is not forced to act like his dead wife(she literally is already rotten). ALSO THAT IS NOT SEX WORK, that is service work(renting a service strictly forbids sexual relations between clients and their handlers)