As public as he is, Warner's would obviously know of them, so there's no "Learning about them"
Actually, I can absolutely believe that the editor who commissioned the story didn't know about Card's militant homophobia. In almost every conversation I've had with people outside of the fandom bubble about why I won't financially support Card's work any longer, the people I spoke with simply weren't aware that Card wanted sodomy laws prosecuted and governments that legalize gay marriage overthrown by any means necessary
. Here's the thing. Card is a big fish in the small pond that is literary science fiction. Outside of that pond, Card is nothing. He's not, by nature, a comic book writer. For people who care about Card and gay rights, they would know. For people who only know that Card is a big name in science fiction circles, they probably wouldn't know. It's entirely possible that DC's editor didn't know about Card's politics.
It's like the recent kerfuffle over Train and Carly Rae Jepson being booked for this Boy Scout Jamboree, and then both backed out after they were made aware of the BSA's ban of gay Scouts and leaders. Both issued statements that they didn't know. People responded, "But how could they not know?" Simple. If you didn't follow the Boy Scouts in the news, it's entirely possible not to know.
Just because there's more information out there, that doesn't mean that more people know it. It's actually easier now to be more selective in the news and information one gets. The Internet builds better epistemic bubbles.