Most of the airline crews that position with us..mainly UK and Canadian charter airlines, are generally in Club, as a matter of course. I know that at least 1 major UK charter airline pays for its crew to travel club, as they naturally have to be somewhere on a deadline (i.e to operate a flight), and club pax would normally be top priority if anything went wrong with the flight i.e weather delays etc...they would be the ones to be transferred onto other flights/carriers first.
Generally speaking though, its is the ground staff's decision whether to upgrade, and that is based on overbooking of traveller..and its is generally the executive card holders that would be given priority, followed by ticket holders who have paid the most..which I guess makes sense.
Hope that helps.
