But didn’t the chef literally serve the dictator, pushing moral concerns aside by dispassionately performing their assigned tasks?

It depends. If one is Iraqi and Saddam asks him to be his chef, they're not refusing. They're probably dead if they refuse. Chef's are also sourced from other countries without disclosing the actual client. Once they land their situation is precarious and getting out is next to impossible. One just shuts up, cooks and takes the money.

It's like everyone else serving the dictator. They money may be good, but threat to life is real and scary.

I wouldn't vilify them. It's the proverbial golden cage. They can't get out even if they want to.

These chefs are effectively being held hostage. One had his passport withheld. Another was executed for giving a kid a stomachache. This isn’t careerism.