You know, I don't think there's ever been a specific FAQ point about them, beyond the game material calling it a panfandom game and all the info being geared towards fandom characters - or if there was, it was trimmed out before we got here! That said, it's been roughly ten billion years since we've polled the playerbase about allowing in OCs and DWRP's broad cultural opinion towards them has pretty well softened during that point, and I know neither of us mods are against the idea of polling for it again at some point soon.