I don't think there is a way to prevent certain sims to walk around and show up on lots (either commercial or residential). The only one I know of is the customer controller for sim-owned businesses, and even then I'm not sure it works for home businesses.
I too would like to be able to prevent certain sims to walk around the neighborhood. It's just wierd when my asylum residents show up around town in their institutional garb... or when I happen to catch one of my sims chatting with them on the computer (a computer to which they have no physical access to in the azylum). Ah well... at least when they steal and run away with the paper... it makes some sense.
EDIT: on the other hand, if the thing that is bugging you the most about having a servo freely walk around is their appearance, you could change their appearence to look like other sims, or use an android-like skin (that's what I do).
Tutorials:
http://fandom-geek.livejournal.com/21455.html
http://www.moreawesomethanyou.com/s...hp?topic=4334.0
I personally use a combinaison of both techniques to make my android servos.