In a pair of separate interviews this week, Arrow writers and executive producers Marc Guggenheim and Andrew Kreisberg have expressed an interest in having Justin Hartley--who played Green Arrow on Smallville--appear on the upcoming series from the CW Network.
“We have some funny ideas for how to [bring in Hartley],” Andrew Kreisberg told Green Arrow TV earlier this week. “More than anything, Justin has been so amazing and so supportive of this. Neither of us really knew him before we worked on this pilot. We actually met him during pilot season, and he’s just been so cool, saying ‘I’m happy for you guys,’ so great… and he and Stephen have actually developed a nice friendship. So, we hope, in the same way that in the Superman movies, you’d see actors from previous incarnations joined in some way… if there’s an opportunity down the road for Justin to play with us, that would be great.”
That's not the only mention of the question, either--in a blockbuster interview with IGN wherein Marc Guggenheim talked about the possibility of bringing Batman to Starling City, the producer said, "I really want to have Justin Hartley on the show in a cameo, and everyone will hopefully laugh and we come up with a clever enough cameo."
Fans online have speculated that it could be fun to see Hartley join the show as someone like Roy Harper or Connor Hawke, but neither of those seems particularly likely; not only would they be recurring roles that probably wouldn't suit the needs of Hartley or the show, but he's obviously age-inappropriate. And there's none of that humor they're alluding to above.
You know what I could see? Travis Morgan (better known to comic book fans as The Warlord), who had one appearance in a Green Arrow comic--but an extremely memorable one!