It took me a while to figure it out but you have to hold LT and look at them until it tells you the target is either invaild or it accepts them and is added to your mission's checklist. Also to gain more artisans for your homestead you need to do homestead missions, these missions should show up in the cities, the Frontier, and the Davenport Homestead. I started to do all of the Homestead missions by Sequence 11, so I'm not sure if you need to continue with a story mission to unlock more Homestead missions.
Demos are like conjugal visits. They give you a taste and then snatch it away, leaving you wanting more. - Ethan, CtrlAltDel
You need to scan them DOING something, for example, lumber workers examining a stockpile of wood. It needs to be part of their work, just aim at them when they are doing that and it will count. You'll need to see all 3 of their actions for it to be completed.
A better example would be the wood carpenter examining a chair he's made.
Took me a while to figure out, but you're not scanning the people, you're scanning the activities they do.