Yes, I have him manning a bar now, and I had him picking Mutfruit before I moved him. Some of the NPCs (example: Marcy Long) won’t actually always visibly do their assigned task, although even those you still get the happiness bonus as if they were. But Preston actually does what he’s assigned.
One thng I am really looking forward to in that Bethesda DLC is those stocks they show Mama Murphy in. I hope that’s real as I want to put Marcy Long and her husband in those.