'Clogged air filter will affect performance(It will be a "DOG" on rollout)
(and cause lots of smoke from unburned diesel in the exhaust).

If by "Breather Hose" "On the air filter housing" you mean the vent hose
line from the top of the valve cover to the top of the Air Cleaner?
If THAT hose is missing or disconnected, you will most certainly have an
oil mist from the valve chamber introduced into the engine compartment.