Dogster.com says that pickles are not toxic to dogs, but most dogs' digestive tracts do not appreciate the excessive amounts of salt and vinegar present in pickles. Burke Veterinary Clinic recommends feeding sweet and dill pickles to dogs as part of a weight-loss diet.
SF Gate explains that pickles are cucumbers that have been soaked in vinegar and brine. Dogster.com says that peeled and diced cucumbers are an excellent snack for dogs; however, as SF Gate explains, while pickling preserves many of the nutrients and fiber present in cucumbers, the final product tends to be very high in sodium. This can cause health problems if consumed in excess.