Embroidery on a blanket is done very similar to embroidery on a Jackets (jacket backs).
Using either the Border Sash device or the large tubular hoops, you should be able to hoop large, thick items such as horse blankets or jacket backs.
Tensions on your machine might need to be loosened a bit to make a thicker, looser stitch. Also increasing the densities in the fill stitches or column stitches will help fill out the embroidery.