Sure, if the rider "responded" well to Clen (meaning the drug produced desirable effects on his organism) then there's no reason to think that it wouldn't have been used during training, in controlled circumstances minus the stress of racing (not to say that the training would be easy, but just that they wouldn't have to worry about the variable of competition when managing the clenbuterol cycle).
It's a harsh product though, and causes some legitimately problematic side-effects. A rider such as Contador, who has total control over his racing program, could get away with using clenbuterol during the season, such as in a period b/w major races when he had the luxury of not having to ride any other competitions. But a domestique w/ a heavy racing schedule would have a very difficult time both tolerating clenbuterol during the meat of the season and evading detection in controls. Of course then one can argue that micro-dosing would come into play, but at that point, I'd circle back to my original argument and posit that there are other drugs that produce similar effects that could be substituted at that time.
Regardless, it's a disappointing situation and whether Contador is sanctioned or cleared, cycling doesn't win.