I think the reason Dixon fell to the 6th round is that there are plenty of plalyers out there with similar skill sets, and his combine numbers weren't that good. Give him better combine numbers and he's probably drafted near Hardesty and Tate.
Among those 3, Dixon, Hardesty, and Tate, the ones that will make a living in the NFL are the ones that work the hardest. I don't think any of them have great enough skills to make it for a long career if they don't find a way to separate themselves from the other backs out there with similar skill sets.