There's a purpose in seating nonrevs in exit rows IF IF IF the nonrev is a FA or pilot as they would be very familiar with emergency procedures such as how to open emergency exits and help others to evacuate the aircraft. This is even more true if the deadheading or offduty crew are wearing DL uniforms. OTOH, other NRSAs (buddy pass riders etc.) should get the least desirable seats, although this might not be explicit policy. It's good for DL's business to treat its paying customers well when there's a choice between such passengers and DL friends and family.