You technically can wear a life jacket snorkeling, but a snorkel vest will provide you with a better experience. While life jackets will keep you afloat, they are designed to hold your head out of the water and make it difficult to float comfortably on the water’s surface with your face down.
Snorkel vests, on the other hand, allow you to swim freely with your head in the water and easily view the marine life below. For more details about why snorkel vests are the best flotation devices for snorkeling, take a look at our article comparing snorkel vests and life jackets.