I know if you build a random feed trough it can attract brahmin to a particular settlement, even if there weren't any brahmin to begin with. If you build a dog house and drop a dog bowl in front of it would it attract a stray dog to your settlement? I randomly had some guy offer to sell me a dog and someone else offered to sell me a brahmin, so I figured you maybe dogs could randomly show up to a settlement with the right things there.