can someone collect social security and file for unemployment?

Sure! He is entitled to Social Security and unemployment does not effect it at all. If he is entitled to unemployment, he can draw that, and if he does find a job, he can earn as much as he wants without effecting his Social Security.
Note that people who receive SSI, Supplemental Security Income, which is a needs based program, do have to report ANY income, and it would effect their payments. But Social Security, based on someone's work, never is impacted by unemployment.

He is drawing Social Security because of his age -- not a disability (SSDI) or a combination disability and poverty (SSI). He can draw unemployment and Social Security at the same time. If you wish more information the Social Security Administration website (http://www.ssa.gov) has a lot of information that can assist you.