A new viral website in support of Geoff Johns, Gary Frank, and Brad Anderson's DC event Doomsday Clock seems to confirm that the events of the 1988 DC crossover event Invasion! took place in the post-Rebirth DC Universe.
The question of what does and does not "count" in DC's decades-long continuity has been one that has driven discussion by fans and the comics press since the publisher rebooted their publishing line with 2011's The New 52, a failed experiment in making the universe more accessible and the heroes younger to woo potential new readers.
DC's previous reboot, following the events of Crisis on Infinite Earths in 1986, was just as controversial but widely considered more successful, with most of its major effects lasting about 20 years and then being reversed in a story that was explicitly a sequel to Crisis.
The post-Crisis DC Universe did not feature many aliens at first, and the first major alien-invasion story came in 1988 in the form of Invasion!, a story in which a group of agressive alien races from throughout the DC Universe came to Earth to demand the surrender of the world's metahuman population.
The invaders were led by a group of particularly gruesome aliens called The Dominators, who were the titular invaders in The CW's TV version of Invasion!, which aired in December of 2016 and featured characters from Supergirl, The Flash, Arrow, and DC's Legends of Tomorrow.
Prior to the invasion, readers had never heard of the idea of "metahumans," and the metagene -- a latent gene which could create superhuman abilities in a small percentage of the population -- became the centerpiece of not only Invasion!, but other DC stories down the line as well. Narratively, it provided writers a way that, like the X-gene in Marvel's mutants, characters could be easily "turned on" without need for an elaborate backstory.
“The metagene, a genetic anomaly found in up to 12% of the human population, was discovered during the Dominator Invasion,” says a report marked as Local News, suggesting that The Bulletin is headquartered out of Gotham City. “This anomaly seems to be a step further from the human fight-or-flight response; when a traumatic or potentially lethal incident occurs, it can trigger the metagene, altering a person’s genetic disposition and causing the development of superhuman abilities.”