Those were far from the only in-jokes on those files. Generally speaking, if you're seeing a name onscreen that isn't relevant to the plot, it's probably a crew member or someone with some connection to the show. It's a fun Easter egg for the folks working on the series. Sometimes the in-jokes are even more relevant to the episode, though. The villain in "Beware the Gray Ghost" is a mashup of BTAS series producer Bruce Timm and WB background artist John Dymer, who were both big toy collectors. And there's a character in another episode who was modeled after the show's Standards and Practices guy.Useless trivia: Diane Duane's name popped up in an old episode of Batman the Animated Series. At a little over 9 minutes into "The Strange Secret of Bruce Wayne" her name can be seen on one of the files in Hugo Strange's office as Batman rifles through it. "K. Jeter" is also one of the names listed.

In-jokes like that wouldn't be added by the writers. It most likely would've been whomever storyboarded that particular Act.That episode was written by Judith and Garfield Reeves-Stevens.