Incorrect. Emmitt Smith was indeed from one of the Vikings picks.
Actually they did not use the Vikings pick (#21) to choose Emmitt Smith. They traded it along with another pick of theirs to move up 4 places to pick Emmitt Smith (#17), but after looking at what they did get for the picks, it was more than I realized, so I'll back off my earlier claim a bit.
http://en.wikipedia.org/wiki/Herschel_Walker_tradeStill Miami has already receieved 4 picks from trading away Marshall and Davis. It's certainly still within the realm of possibility that they get a few players that could be valuable to them.