I'm not sure about all sports by any means, but I doubt the elite college team for the more prevalents sports in the US (baseball, football, basketball) could expect to beat the elite pros. I don't know about hockey or soccer, but I would expect the elite amateurs to be roughly equivalent to the rookie pros. I have no clue about something like curling because I'm not aware if there's a professional league...there may be in Canada, I honestly don't know. I'm fairly certain there are no professional bobsledders or lugers although I suppose you could call Shawn White a profesional snow boarder....but yet, aside from the olympics and endorsements, I'm not sure how he makes a living at it (unlike professional atheletes who make millions per year).
Going back to the dream team, I don't think there was a team anywhere in the olympics that had a chance.