Naming slaves/mercs will be abused, just like if faction names were opened up. Using +requesthelp to ban people for such things just wastes the GMs' time and reduces their ability to respond to actual problems in the game. Selecting from a list of names isn't a bad idea, but if it were accepted, would probably be dead last on the to-do list. But I agree with choosing their dialog. You could tell them how to act, instead of telling them the exact lines. You'd choose from different styles:
Friendly : "Hello, wastelander." "How are you?"
Territorial : "You should leave." "Get out of here before I blow your brains out."
others, but I can't think right now.
This way, abuse is avoided, and it also reduces server resource consumption because there's only x amount of predetermined lines, instead of having to store every line, including similar variations.