Yes, Gacy was given the honor of posing for a photograph with the first lady, and Mrs. Carter even signed a copy and wrote "best wishes" to a man who would turn out to be evil incarnate. If you look at his jacket, you'll see a pin that indicates the Secret Service had given him special clearance to meet her.
A few months later, Gacy was arrested, and the remains of most of his victims were found in his home, which proved to be most embarrassing thing to happen to the Secret Service until several of its members decided to give some Colombian prostitutes an extremely thorough body cavity search. Sure, it's not their job to enter the homes of everyone who gets a photo-op and rip it apart in search of dead bodies, but Gacy had already spent time in an Iowa prison for coercing a teenager into sex and then paying another teenager to beat the shit out of him when he went to the police.
Gacy had kept his conviction a secret when he moved to Chicago, and you couldn't just look up sex offenders on Google in the 1970s, but if there's anyone who should have been capable of digging this information up, it was the Secret fucking Service. He didn't even change his name!