Earlier quoted context omitted.
Except the divers are probably Marines. Enemies which are probably well trained and armed. No Dolphin will bump on them and place a device on their back...
You have evidently never dived. Even the biggest, roughest, toughest marine diver would be outclassed by a juvenile dolphin with regard to mobility. Let alone a trained one who didn't want you to touch it.
You assume too much on Internet. Dolphin isn't really known by their fine work with their "mouth". I'm wondering how it would place a buoy with their mouth on somebody's back..