I actually remember quite well that in the cases of both Helu and Ameer, that there was plenty of questioning their being recruited to play running back by some on this board. Not naming any names, because I can't remember any, but I do remember both being questioned quite well.
In both cases, we already had committed higher ranked running backs in the class, and it was just assumed those were the guys and there was no reason to go after others, at least by some.
For Helu, it was Quentin Castille that was the higher ranked RB, and we all know how that turned out. I even remember speculation from some that we were recruiting him to play LB (I think some services may have had him as an Athlete, though Rivals had him as an RB), because there was no way he was going to get much playing time with the great Quentin Castille around.
With Ameer, it was Aaron Green that was the big time recruit. Much like Helu, I remember speculation from some that he was being recruited to play defense (Rivals had him as an athlete).
The point I'm making with this is that it's never 100% how a player is going to turn out, and obviously stars are useful, but aren't the end all. I'm not completely anti star rankings, I always point out in regards to star rankings that both Vince Young and Reggie Bush were 5-Star and top ranked (VY was #1 in the nation in 2002, RB was #2 in 2003), so clearly they get them right sometimes. But, as is evident in this thread, sometimes they don't tell the whole story; and lowly 3-star guys end up being the Star, and the big time 4 and 5-stars don't pan out.