If the ball touches the line, the ball is in. However, the ball has to touch the line! The pickle ball does not compress the same way a tennis ball does, so many shots that would appear in to a tennis player may be in fact out. There is one exception though, if a ball touches any part of the NVZ (kitchen) line during the serve, the ball is considered out.
In general, the players make their own line calls, even when there are referees officiating the game. The team on who's side the ball bounces makes the call. The other team has the right to question the call but the team that made the initial call has the final decision. If none of the players saw the ball clearly or are unsure about the call, the ball is in.