On the cuck route she works for Darrel in the Gym. Jenna suggests that she becomes an adult model, and Nat says she'll think about it. But nothing ever comes of it. And then later Darrel drops by to offer her a job at his Gym.
The only way to get the modelling content, is by Nat living with Jenna and Sam on the NTR route, after Ethan asks her to leave. Obviously, on the cuck route she's still living with Ethan, so it's impossible to get that content on the cuck route, whatever choices you make.
As far as Darrel is concerned, No 1 wouldn't apply on the NTR route, because Nat and Ethan are no longer together as a couple on that route, after Nat and Darrel's date. Ethan has washed his hands of Nat completely, and doesn't consider her to be his wife anymore. So what you suggested above wouldn't make any sense. They basically stop seeing each other for no discernible reason. Now I think I can guess why this might have happened, because the Dev wants to concentrate on Nat's friendship with Jenna and their ensuing adult modelling collaboration on the NTR route? All of the routes seem to have one person who plays a bigger role, than others. On the Cuck Route, it's Darrel, on the NTR route, its Jenna, and obviously on the Peter route, it's Peter. The issue I have, is no reason is given for Nat and Darrel's blossoming friendship, suddenly vanishing without a trace on the NTR route