http://www.rotoworld.com/player/nfl/4661/glenn-dorsey
Prior to joining the 49ers, Dorsey was the Chiefs' starting right end in their 3-4 scheme.
Maybe he lined up at NT on a few downs, and that's what you saw, but I'm going to go with what Chief fans are saying as well as the site linked above. Lots of Chief fans were upset that he didn't produce more in terms of QB pressures. They say that if he was able to do so, he would have been lined up at nickel DT in their sub packages, but he was not.