Calling the assassins the Long Bow Hunters is a nod to the limited series "Green Arrow, the Long Bow Hunters" from 1987. The Arrow show owes a lot to this series as it moved the Green Arrow character in a darker direction moving away from trick arrows and gimmicks to traditional arrows, just like the show. It also introduced Shado and Eddie Fyers also key characters in the Arrow series.
When Oliver speaks with Rene about when they first met, he says "I thought you were just a thug in a ridiculous costume." Rene's original costume was a hockey mask and scruffy clothing; the same kind worn by the character Casey Jones, portrayed by Stephen Amell in the TMNT 2 film.