Heck, Brandon Routh is playing Ray Palmer on ARROW these days.
Well, yeah, but that's not quite as on-the-nose as Shipp playing his former character's father or Slater playing her former character's aunt-in-law. It's another DC character, but not one that has a direct connection or relationship to a character he played before. It's more akin to, say, getting Roger Moore to guest-star in
Alias.
(And by the way, I'm liking Routh immensely better as Ray than I liked him as Superman. Maybe if he'd been allowed to play Superman in an upbeat and fun way like this instead of mopey, stalkery, deadbeat-dad Superman, I would've liked him more. I still think his voice is way too nasal for Superman, though.)