Some years ago they worked AFAIK and it contributed around 2-4% to each ability to each sailor.
Normally it was only used on fighter CVs to max out the fighter ability. BBs better use another engi or repairer in that support slot.
How to check.? On a BB your guidelines should become longer and overheat time a little increased (is shown in port above sailor list). But the seaman needs higher level and vets/experts to see a difference.