I received this dog with a bonus of 3x Objective completion. I have attached the dog to a dweller and trained the dweller nothing special happened (I didn't get three x the bonus points). I completed an objective with the dog attached and I didn't get three times the caps. What does this bonus do?

objective: get 5 females pregnant. With dogmeat, you will have triplets in one pregnancy etc.

Do you actually get 3 babies or simply you score as if you get 3?

you will score 3 points instead of 1. If you have 1 female pregnant, it counts as having 3 females pregnant. You level-up 1 dweller, it counts as leveling-up 3 dwellers etc...

Neat. Triplets would be really cool, though.