Green’s Dictionary of Slang

all-night man n.

[ext. use of SE, i.e. he is working all night]

a body-snatcher, a ‘resurrectionist’.

E.B. Ramsay Reminiscences of Scot. Life and Character (2nd series) 133: I have heard quiet and worthy men speak of the body lifters, or ‘all-night-men,’ as they were wont to be called.