Zod and Faora's son, Doomsday, abducts Lois Lane's cousin, Chloe Sullivan, from her wedding to Jimmy Olsen at the Kent farm. Before the abduction, Lois discusses her feelings towards Clark with her ex, Oliver Queen. Tess Mercer, illegitimate daughter of Lionel Luthor and half-sister of Lex Luthor, was on the island with Oliver. Of these eleven characters, only three were specially created for Smallville although all the relationships between the characters have changed.
In Arrow, Shado, Shado's father and a version of Fyres were on the island with Ollie.
Addendum: I should have mentioned Lana Lang who, like Ollie, tracks Lex and shows at the wedding. There is a sense of important events occurring again.