Is ocean water okay for dogs to drink?

no they will become dehydrated and violently ill

Ocean and any sea water can unfortunately be fatal to dogs - there is a story of a poor dog dying from taking in too much sea water whilst swimming - see link. Sea water can cause extreme dehydration and symptoms of sickness and diarrhea. A dog life jacket will keep the dog's head above water and therefore there will be less risk of the dog ingesting sea water. Short muzzled dogs such as boxers are more at risk and again the answer is to use a dog life vest to elevate the muzzle.