My seats had hog rings everywhere, it seemed. Even places I would never have thought to put them (and a few mistakes/misses). They had a few holding on just the burlap that has the wire in it. The foam is hog ringed on in the areas where the covers are held in to the spring's strait pieces of wire (the slits/cuts/pleats in the foam). The edges of the foam were ringed to the springs in a few places that didn't have that extra "paper" type materal "flaps" on them. But I really had to take a lot of pictures as I disassembled them. Plus, have everything on had to take many looks to refresh my memory... I found it "easier" to assemble the foam and cover to the bottom springs before attaching the springs to the frame (not that that was very easy!).
Anyway, I guess the answer is yes, there are hog rings through the foam and burlap that attach to the wires. Again, mine had a few hog rings in those areas w/o the covers included... Then, I went up through the bottom of those slits/pleats to ring the seat cover wires through the foam and burlap to the spring wires.