If someone is working a full time job (the currently employed are definitely targeted in the article), and are 'experienced'/older, and thus more likely to have other demands on their time like wife/kids, contracting, even in off hours, becomes more difficult.
It won't be impossible to 'audition' but it will definitely be tougher.
(To say nothing of the intellectual property issues if the possible employee is in a related field and the employer is peeved at them leaving.)
If I was at a stable, good job, and wasn't looking, and someone was trying to poach me with the siren call of 'contract to hire' or 'work this weekend', well, it'd be an uphill battle for the poacher.
Maybe that's why I'm not in the Bay area, working for a startup :).