Cody Glenn actually entered college as RB, but eventually won the starting weak-side linebacker position for Nebraska last year. Although he has very little experience on defense, he has played both OLB and ILB spots. Glenn has prototypical size for a Colts linebacker (basically a slightly bulky safety) at 6' 0", 244 lbs, and he ran a respectable 4.67 40-yard dash at his pro day workout.
Once Ed Johnson's one-week suspension has been served, the Colts will have to release another player. My guess is they'll release backup K Shane Andrus or one of the two backup QBs, Jim Sorgi or Curtis Painter.
Speaking of suspension, Cody was held out of 2 games last year for "violating team rules" which was rumored to be him selling his game-issued tix, but ESPN has reported that was false.
Update #1: Colts just claimed S Aaron Francisco from the NFC champion Arizona Cardinals
Update #2: Colts just waived Cody Glenn. Awesome.
Update #3: Cody Glenn placed on practice squad. Riveting, I know!