Foreign Retiree working and still paying into social security?

My husband is a foreign retiree receiving monthly pension from Germany. He has a social security number but has never worked and paid into social security in the U.S.

 

Is it right to think that it will be a waste for him to work for a business and pay into social security and medicare from every paycheck considered he will not be working for 40 months during his retirement year to qualify for social security?