I'm 100 percent certain that J'onn J'onzz showed up in Smallville I just don't remember the episodes (I know they were the later seasons of the series). I think it's really cool that he's the MM. We'll have to see what that means.

CLARK: No. I'm just worried I'm a jinx.
JONATHAN: A jinx?
CLARK: Yeah. Let's face it, ever since she's known me, Lois's been kidnapped, frozen, pushed off buildings, almost stabbed, poisoned, buried alive and who knows what else, and it's all because of me.
-"Contact" (You're not her jinx, you're her blessing.)