Sounds like a master-slave domination sex game they both played, which looks bad in the rear-view mirror when put into a scary-sounding context by an attorney.
Seduction isn't grooming. Grooming is a word used about minors, not adults.
The two participants clearly both agreed to play the game. That's why they had a safe word. So the fact they engaged in this activity was clearly consensual.
From what I can see, she placed herself voluntarily in the position she is complaining about after the fact.
Sounds like there's no evidence that he acted without her consent. Just text exchanges which can be construed as role-playing.
If he forced himself on her when she used the safe word or if she split up with him and he forced himself on her, then there's a case. Otherwise, I think it has the look we often see: of someone that is trying to get a payout from a wealthy person so that that person can avoid the embarrassment of a court case.
Hell hath no fury like a person looking into someone else's pockets and thinking they can extract the money.
Morally, he is an arsehole, because he is married. Legally, looks like a weak case to me.