That's an interesting concept...if you've ever read 'Memnoch The Devil' by Anne Rice (and before anyone feels they need to point it out, as much as I would love to meet Lestat, yes, I know Anne Rice writes fiction) there is a very similar idea out forward in that.While Memnoch - as he calls himself - does have free will, his job as 'The Adversary' is to ensure that as many people as possible make it into Heaven. Except he's a little sick of being vilified and wants to quit.
The thing I always find odd about Job (haha...oddjob) is that if Lucifer has been cast out and is the enemy of God , what is he doing swanning about Heaven unmollested, making bets?
If I throw someone out of my house and they are truly my enemy, I'm not going to be making bets with them if they turn up in the lounge room...I'll be on the phone getting the AVO enforced.