Yes. I do. Watch his fights with Mirko and Big Nog if you need some proof. When he was at his best - fast twitch, aggressive, great grappling and reflexes, awesome recovery, he could beat any heavyweight who's ever lived.
You mix in the fact that JDS is not good defensively backing up, I wouldn't be shocked to see him get knocked out. The pressure he would put on Junior wouldn't allow him to dictate pace and distance or take control of the octagon. Fedor in someone's guard in his prime is a scary sight.