I think there's a lot of exceptions. Eva Braun (Hitler); Mrs. Kruschev; Ms. Chavez. It depends on the dictator--whether he likes to "share."
Interestingly, the most meddling of dictator’s wives tend to be actresses. Mao’s second wife was the one who instigated the Cultural Revolution which she used as a guise to get payback against people who had slighted her or denied her a role. Same with Eva Peron.