The Hennessy Expedition is made with 200d Oxford Nylon (actually 210d, but that's a rare #). Oxford is another type of weave, as opposed to Ripstop or Taffeta. It's very strong and quite abrasion resistant.
Joann's doesn't give any info on their website as to what sort of weave or weight their Sport is. It very well may be 200d Oxford (200d is pretty standard for Oxford). Oh, and I was wrong in my previous post, their Sport material is type 6.6, which is the higher quality (opposed to type 6) - so that's good.
My guess is 200d would put it in the 3oz/yd+ weight category. Plenty strong for a hammock and should carry lots of weight safely.
We really need a Definitive Fabric "What's What" Article here. I'm certainly don't know enough to make it definitive, but maybe I could get it started sometime soon, and add/edit as necessary.