Special Teams units must include 1 player from your draft class that was a kick or punt returner. If you notice my example using the 1999 Rams Special Teams, Dre Bly was drafted in 1999 and returned kicks that year.
If you wanted to use a stud special teams player, like Steve Tasker, I have o problem with that. Just make sure they were drafted from your year and you're using the correct special teams unit.
Kickers and punters do not count towards special teams units. They are separate positions.