From another perspective, you could also see this as betting on someone, which is actually kind of fun (if I understand correctly and you double your money if they're hired). If they provided accurate statistics on the amount of their candidates who end up being hired, it might not even be a bad investment. I'm curious what the legality of that is though, it seems like actual betting.
I also think friends and online acquaintances might be a bigger source of 'bets' for them than former colleagues. Or even people you don't know, but they know of your work on open source projects, etc.