If your aquarium is well established, I would go ahead and obtain some peppermint shrimp (Lysmata wurdemanni) and introduce them to the tank before the seahorses. That way, they will be the established residents of the aquarium and the seahorses will be less likely to regard them as potential prey when the ponies are introduced to the aquarium. (Large seahorses will occasionally attack small decorative shrimp as if they were feeder shrimp, and adding the shrimp first decreases the chances of that happening somewhat.)
However, if the aquarium is still fairly new, then I would hold off on the peppermint shrimp for now. Cleaner shrimp and decorative shrimp in general do best in mature tanks with good water quality that have had a chance to stabilize and settle into a state of equilibrium.
Best of luck stocking your aquarium, Don!