I am not really that familiar with Tangle Tuft however it looks like a wonderful textured material to work with! I assume that most people might use it as a filler or a veiling type trim or even fray the edges a little more to add some extra texture! Like you said i am sure it would work fantastically with Sinamay.
I know this as cobweb sinamay so you can block with it like normal sinimay. I have also used heat bond to fuse two pieces together and shaped it over hat blocks that way - no extra stiffening required as the heat bond does the job for you. You can also fuse a piece of normal sinamay within it too.