Well there is no pressure with snorkeling so I can't see why not. Generally they say don't do things were you could get injured - eg paragliding, jet skiing, whitewater rafting etc
I'm sure if you use your common sense you won't have any problems. Just be extra careful of food and water issues and you'll have a ball.
Go and enjoy yourself while you can. If this is your first child - lie by the pool and read a book. It'll be the last chance you get for a year.