I have friend who has inoperable cancer and there are no treatment options that will offer a cure. He has been self-employed for quite a number of years and is presently only working part-time. He has paid into Social Security over past years and has enough credits to receive disability benefits, but can he receive those benefits if he hasn't filed recent tax returns and owes taxes from prior years, as well?

He can only get in trouble with the IRS. The two agencies are exclusive, unless he owes the taxes and has gotten a notice from the IRS that he owes. If he files those taxes and pays the SSA tax, he may get an increase in his benefit.