Ok,
here's a full study from 2005. According to this, college OL were among the highest % of any position to have ACL knee injuries requiring surgery.
And another from 2019. This one just shows that college OL ACL injuries occur somewhere in the same rate as other positions. It's discussing the return to play rate, and states that OL are amongst the fewest to make it back.
I can't guarantee that all of these OL wore braces, but considering that a majority of college OL do, I'd say it's pretty reasonable to say that many, if not all of them, were wearing braces when they tore their ACL.
I found an article talking about Dr. David Chao saying he recommends all OL wear them, but he's also the guy that stabbed Tyrod Taylor in the lung, and has multiple other marks against his record in his past, so I'm not exactly sure how much I trust him in general.
I can say from my own experience in wearing knee braces and playing OL, they're ****. They limit your mobility significantly and I felt far more prone to having my leg being put into a compromising situation than without them. They're really only useful when you've had a sprain or injury and need additional stability to give you support. A healthy knee does not need a brace.
I said it before, but no brace would have saved Lewan. Braces only possibly help provide stability to a healthy knee when you have outside forces acting on the knee. He landed in an awkward, twisting motion that was from his own body putting force on the knee, not someone coming in from the outside.
I'm sure there's some evidence to show that knee braces can protect in some situations. But I think of it this way: would you rather be in a big truck that may provide better protection in a wreck, or a sports car that has better breaks and control and allows you to avoid some of those accidents altogether? There's not necessarily a right or wrong answer there. Some accidents are unavoidable. But some are. I'd personally rather have more control over my situation and have fewer wrecks.