No, professionals can take part.
The orginal idea was that the Olympics would be amateur, but by the 1970s all countries were abusing this. Soviet athletes were given officer's rank in the Red Army but never served a day, they just got paid to practice full time, the same for other athletes from behind the Iron Curtain. In the Free World, corporate sponsorship and fake 'spokesperson' position were used to accomplish the same thing.
Recognizing that amateurism had become a farce, the IOC voted to remove the amateur requirement in 1986. They then made each sport's international federation responsible for determining who was eligible to participate in their sports.
Since then each of the sports in the Olympics has gradually gone professional except for boxing. NHL players began participating in 1998.