I don't think they could have not known that O posed a material risk on this front.
He has a long record of over-the-top histrionics, going back at least to when he pounded a Colonel Reb pin into his bare chest during his time at Ole Miss (O seems to have a thing about taking his shirt off in public), and numerous incidents since then entirely consistent with recent antics.
My guess is that the LSU PTB hoped he had matured out of that. And winning a NC masked some of it -- what's embarrassing for a loser can be endearingly eccentric in a winner.
But even they were embarrassed by his behavior on the field and in the locker room after they beat us in 2019. I can't link those episodes due to some pretty salty language. But they're easy to find on YouTube for anybody curious as to exactly what he did and said.
Yeah, some of that might appeal to 18-year-olds on the recruiting trail. But they're not typically going to register that it's entirely inconsistent with a winning culture or approach to the game. There's a reason top coaches don't act that way, and it's not a lack of testosterone.
From my recent visits to LSU boards, it appears that 2019 only gave O a bullet-proof image of himself, and he's been alienating a lot of important people with his over-the-top macho arrogance ever since. But 2019 bought him a pass, at least for a while.
So to circle back to the original point, even before they hired him, there's no way the LSU PTB didn't know that O was a huge PR risk. They hoped he'd matured out of the worst of it, and that winning would make the rough edges points of endearment, not embarrassment.
It's an understatement to say that it hasn't worked out the way they hoped.