If a person is treated for hip displaysia at birth will he never have problems later?

Not necessarily. The goal of early management of hip dysphasia is to minimize the long term effects of the disease by altering the environment about the hip in an effort to gain and maintain as much painfree function as possible. Treatment in no way negates the possibility of problems in the future. I saw two patients just today that had successful surgery as children that now need resurfacing or hip replacement.
Maybe. Most patients who have hip dysplasia treated successfully before the age of 2 years will probably not have problems later in life. X-rays can give some information about the state of the hip, but are not totally predictive.