Why are you asking if he MAY file a return instead of is he REQUIRED to file a return?  A person who is another person's dependent  does not have to file a return if his only income is social security benefits. 

The money you hear about people getting for just filing a tax  requires him to  have some earned income (wages or self employment) and be claiming child dependents. A child or disabled person does get anything from the government just by filing a tax return. Dependents are not eligible for the "refundable" Tax Credits.