I can't really see what he's doing, but one of my yorkies has rituals she does before she goes to sleep, which involves licking mine or my husband's arm. It seems to soothe her and then she falls asleep. I too have wondered if it was some carry over from when she used to nurse.
Sometimes the two dogs will lick each other's tongues like they are French kissing. This will go on for a long time. I've never seen dogs do that before. Maybe I should videotape it and play some Barry White in the background.