http://www.camelbak.com/sports-recreation/hydration-packs/hoss.aspx link to the camelbak website, where it states "The H.O.S.S.™ also features a waterproof main compartment with easy to use roll-top closure (like a dry bag for boating)."

This is a roll-top closure, this you can tell from the picture. I have a Camelbak Vantage 40 with the same roll-top closure. Then it has Velcro, buckles and fasteners. However, it is not 100% submersible, more functional for having rain stay out. You could take it out on the water but it will not replace a dry bag with the same roll-top closure.

I too am confused about this... The camelbak website says that it has a waterproof main compartment. I'm looking for something that will keep my camera dry with enough storage space for a long day hike. Originally I looked into the HAWG NV, but now I'm thinking that it's too small, so the waterproof thing is a big deal with me. Quoting from camelbak site: The H.O.S.S.™ also features a waterproof main compartment with easy to use roll-top closure (like a dry bag for boating).

I do not see where you read that it is a waterproof roll-top bag, it is a zippered water-resistant pack. So, no on the kayaking.