It has not been well demonstrated that probiotics reduce the gas and bloating caused by milk and dairy products in people with lactose intolerance. On the other hand, fermented milk products, such as yogurt and kefir, which contain live organisms (not necessarily "probiotics") have been shown to cause fewer symptoms of lactose intolerance than regular milk containing the same amount of lactose.
More about this is found in the Probiotic Supplements and Kefirs Review >>
Some probiotics have been shown to reduce abdominal pain due to irritable bowel syndrome, as well as functional abdominal pain in children, and colic in infants.
(Also see ConsumerLab.com's Review of Products for Lactose Intolerance — Lactase Enzymes and Lactose-free Milks)