Yes. As explained in the support document you came from, Series 2 and Series 3 apple watches can be used for shallow water activities like swimming in a pool or ocean. That means it can be used in salt water like that of an ocean. Swimming does not need to be an actual breast stroke or the like, it also includes simply wading in and just generally floating in the ocean.
Also as mentioned in the support document you came from, do note some Apple Watch bands are not rated for use in water, and may have adverse reactions to salt water. If going in salt water its best to use the regular sport band.