Pellon 809 seems stiffer than some of the other craft interfacings. I'd worry slightly that if something is sat on top of an wreath made with it, the creases formed wouldn't easily come out. The Pellon or Bosal foam products will spring back. I have both Pellon foam and 809 and would definitely opt to use the foam for the wreaths. I think the Pellon fusible fleece (not fusible batting) may also work okay.
But heck, if you have a ton of the 809, try a couple squares and see what you think. Make 4 and if you don't like them on the wreath, use them as coasters! ;-).