Been using bowlines for safety(fire dept) and sailing 35yrs. Never ever ever seen a proper bowline "shake loose". Can tie it weakside one-handed, upside down, behind my back, in the dark, underwater, while brushing my teeth.
If a diver is attached to an actual haul line (not common, but happens in swift-water recuse scenarios), then they're going to be clipped in via a carabiner, which is tied on with a double-loop figure-eight. The double-loop figure-eight is the standard "if your life is gonna depend on it" knot around here.
(I am not a rescue diver, but do support dive operations from time to time)