Although there are Nosalises when playing as Uhlman, there are not enough to unlock the achievement/trophy as him. Instead, wait until you are in the dream sequence, playing as a young Khan. The best place to unlock this is just after you have defended the barricade with your two companions. Although there are Nosalises here, your companions will likely kill too many for you to make a dent in the necessary number. Instead, wait until you are in the main station with the man called Kuzmich. When he is killed, Nosalises will spawn infinitely, around one every ten seconds. Just run around the station, killing them, and it will unlock.
The attack on the station is based on the Mobius trailer, which did include Big Momma. It is possible that the Nosalis Rhino was planed to be in the level but was removed from the level for some reason, and the achievement/trophy description was overlooked.