Dwight Schultz (Martian Manhunter), Michelle Forbes (Circe) and Wil Wheaton (Robin) previously starred together in Star Trek: The Next Generation as Reginald Barclay, Ro Laren and Wesley Crusher respectively.
In the opening cinematic, Metallo appears combating Wonder Woman. It was originally scripted to have her fight Solomon Grundy. But it was decided that the ESRB would take more kindly to Metallo's beheading.
There is a vampire connection between the voice actors Gina Torres(Wonder Woman) and Circe(Michelle Forbes). Gina Torres appeared in an episode of The Vampire Diaries and Michelle Forbes was a major character in the 2nd season of True Blood. The true connection is that on these 2 separate shows, both died in the same exact manner by having their hearts pulled out.