No, I don't think the Will Smith/Chris Rock matter was staged or planned. For one thing, both of them looked like assholes in different ways. Rock handled the after-slap moment well but if he'd known it was coming, he'd have had a smarter line at the ready…maybe "Is it too late to change my vote for Best Actor?" Smith would not have been caught on camera grinning and giggling at the joke before (apparently) deciding that if his wife was upset by it, he was going to respond with a shot of toxic masculinity.
And how would either man have benefited from staging such a thing? Smith turned (potentially) the greatest night of his life into a spectacle where much of America is thinking he's a jerk. Here's a guy who's at the absolute tippy-top of his profession and he'd go along with a stunt to…uh, why? To liven up the ceremony? To change the discussion from whether he deserves the Academy Award to one about whether he deserves to be arrested? To be a bad role model for immature males? If it had been planned, he'd have had a much better speech, too.
What might be staged is an upcoming appearance somewhere of Smith and Rock together, making nice and acting like it was no big deal. Publicists for both are probably suggesting such a thing. And somewhere, some producer is suggesting they remake 48 Hours with Smith taking over for Nick Nolte and Rock in the Eddie Murphy part.