Income is income. In most cases, you cannot turn away a person because they are in some sort of program. It would be in your best interest to know what the most common programs are out there so you know what you are getting into.
You best 'defense' is to have a defined rental criteria that you use to process your applications. State that you have the right to confirm landlord references and income and have an income requirement (most landlords state that income must be at least 3 times the monthly rent). I also suggest running credit reports. It isn't too expensive and it can save some headaches in the long run. In some states, you can charge an application fee to offset credit check costs as well.