My last project I used Fusion Pro premixed grout, and I thought it contained latex as the sealer, but I looked up the details and it looks like it is not latex based. When I would open a new container, some of the liquid had settled to the top, and it was milky looking, which is why I assumed it was latex based. It is also water cleanup until it sets, after which you need chemicals to clean it off, which also led me to believe it was some kind of latex based binder. This grout performs similarly to epoxy with the ease of regular grout installation. It doesn't need to be sealed and is mold resistant. When I tile the rest of my upstairs (kitchen, living room, entryway, and hallway), I will use this product.
I think Latex works fine with moisture if there is an acrylic in it. After all, my exterior house paint is all latex based, and it has held up beautifully for 15 years now. Definitely not the same as a latex caulk though, and I would never seal anything against water with anything other than pure silicone.