To get a 6th year, you have to after your fifth year, you have to have had two years which were lost to injury under circumstances where you were eligible for a medical redshirt that season. Which means not playing after the 3rd (may be 2d or 4th) game of that year due to injury.
If Bennett were not to play this year, I believe he was eligible for a medical redshirt in either '09 or '10 (eligible -- he took a normal redshirt his freshman yeart) and should be eligible to apply for a sixth year. But if he plays this year, he's done.