This gives me an idea of how to understand a developer's integrity and views on privacy before hiring. Ask them if they're ok with giving you their facebook account. But don't really ask for it. If they ask "so should I write down my password". You just say "I don't really want your account, just wanted to know if you were ok with it".
What? It's not a request to commit a crime, it's a check of the strength of their belief in privacy. There's nothing wrong with the action you're asking them to do.