I don't think that particular play is a great example to cite if you want to criticize Niblett. Go back and review that play if you can -- I have. That was a shitty, low, line-drive punt that landed a good 20 yards in front of where Niblett had set up. Not even Deion Sanders in his prime would have tried to field that punt on the fly. The punt then bounced crazily in OU's favor. Niblett approached the ball and clearly thought about trying to field it, but at the last instant he decided to let it go past him. I suppose one could second-guess his decision not to try to field the punt on the bounce, but with the way (and speed) that ball was bouncing, I had no problem with his decision. There was a good chance that an attempt to field that punt would have led to a muff, and the last thing Texas needed at that point in time was a muffed punt and a turnover in favor of OU, which would have been a huge swing in momentum. And, as someone else has pointed out, part of the reason the drive started at the 5 yard line was because one of the punt return team got called for a penalty.
Some of Niblett's other decisions re: fielding punts in prior games are a lot more questionable than that play, IMO.