You should talk to this old guy's previous supervisor to find out why he was laid off. You may want to bring his previous supervisor for lunch to talk about it. If he/she could tell you something he/she was not satisfied with this fellow then you'll have justification.
Other things you may consider are the salary level, long term commitment, and a trial period.
When you talk to your supervisor, focus on how the decision of whether to hire this fellow will benefit the company, not youself.
