Brady's had a 17-year career in the NFL. Of course he's been concussed at least a few times. Don't forget it wasn't until a few years ago that the new protocols were put in place.
That said, totally irresponsible on Gisele's part to be talking about this. I can't recall a single instance where Brady was checked out by the independent doctors on the sidelines. You know if that happened, the cameras would have panned over and shown every moment of it. I don't think it's ever happened. And if he's never been evaluated in-game, then it sort of blows her statement up.
He took a shot to the head in the most recent Super Bowl, and looked a bit dazed for a sec, but obviously he didn't seem off at the end of that game or in any of the post-game interviews I saw.
The OP's assertion (and assumption) that this automatically equates to "cheating" is unjust IMO. Regardless of whether or not it's even true, making the immediate jump to "well the Patriots had to know about it" is bias in its purest form. I'm not really sure what big advantage you'd have in sneaking a concussed QB into a game anyway.
Plus aren't more than half of you always saying how soft Brady is?