He agreed to let her work during the weekends. And he also agreed to let Sensei work with her. That was it. Sensei clearly wasn't in on them shooting porn at all. The guy said he had relayed it to sensei that he wouldn't circulate that. It's like "I didn't want it to get out by accident, so I didn't record. I also told Sensei I won't spread it". But at no point was it stated, or even implied, that Sensei agreed to this. FMC definitely didn't, and she's the first person that needed to know. Nobody was in on this plan except those two. Also, think about it, brother: He didn't record, didn't intend to record, but drugged her, then NTR'd Sensei for his own satisfaction.
The only thing that changes is that the guy didn't record porn, which isn't really making things better. And even if Sensei specifically agreed to this, and sloppy dialogue just didn't get that across right, that still leaves Sensei as a second, slightly-tamer Kise because he literally agreed to get NTR'd by having his girlfriend drugged and seduced for... no useable product; Basically every work-related NTR bait scene that had been implied played out right then and there for reason that have literally nothing to do with her job.
It wouldn't even make sense for this to be in the contract in the first place, since cameraman going out of his way to point out that a scene like this would destroy her. He doesn't want to destroy her, and presumable Sensei doesn't want to get NTR'd.