Zakaat al-fitr should be given to poor Muslims even if they are sinners so long as their sin is not something that puts them beyond the pale of Islam. What is meant by poor is those who appear to be poor, even if they are in fact rich. The one who is paying the zakaah should seek out good poor people as much as possible. If he finds out later that the one who took it was actually rich, that does not affect the one who gave it, rather he has discharged his duty, praise be to Allaah.
And Allaah is the Source of strength.