I can already confirm that items are picked up when they encounter them.
Maybe you should have given them high-end armor and weapons. The picked up and equiped items could change a lot ...
That's what you would normally do, yes. But I am experimenting. It is obvious that a lower level dweller uses a lot more stims in the waste as a higher level dweller would do.
I do the same, one of the guys who I sent them naked returned with a Hardened Minigun with 19-22 attack (it is my biggest weapon now, I didn't purchase anything from lunchboxes until now)
The other guys returned with Sturdy Raider Armor (better version of simple Raider Armor) and another one returned with Sturdy Combat Armor.
So sending them naked gives them a better luck it seems for me, or just that happened to me. But I lost a few of them and had to revive them to receive those better gear.