I've been wondering the same thing. How did they get around the rules to include NHL and NBA athletes in the Olympics?
I believe I have found the answer.
I remember when the rules were changed, for the summer games, allowing NBA professionals to play basketball. That first USA team (1992 Barcelona) had Charles Barkley, Larry Bird, Clyde Drexler, Patrick Ewing, Magic Johnson and Michael Jordan, plus others.
How proud we were to watch The Dream Team beat Croatia, Lithuania and Puerto Rico! Even mighty Angola could not withstand the onslaught!
(note: I am being sarcastic. I recall not watching any of the basketball games because I thought it was silly. Rather like watching the Harlem Globetrotters beat up on the Washington Generals game after game).
Anyway, it appears that by the 1996 games the amateur status requirement of all athletes was dropped for all fields, except for boxing.
I hope the above is accurate: I did not rely on Wikipedia for any of my information, so it should be close (Sports Illustrated was useful).