I have seen bows that had horse hair, unbraided yarns, ribbons (with or without feathers, and I guess even some with scalp-locks. Believe it's ornamental. Some of the Iroquois speakers had hair on the finials but I believe that was human....most of the horse hair (like from a favorite war pony or a pony taken from an enemy) decorations would have been with the "horse cultures" which a lot of the Great Lakes tribes were not.
After all that, don't believe hair on an Apache bow would be in order, most I've seen were short and plain.....some of the Kiowa/Apache (Lipans) may have had the custom but like I said I have never seen one.
rich