Yes, it is safe and is an area of science that has been researched over the past 100 years. Due to the brains natural tendency to entrain to any periodic stimulus you will already have experienced this yourself with realising. For example the rhythmic crackling and flickering of a fire, the sound of seashore waves rolling in, rythmic drumming and chanting.
The common warning that you find is for people who are epileptic or prone to seizures. This warning originated from photic brainwave entrainment (flashing lights). In fact one of the earliest discoveries was from Apuleius in 125 A.D. who found the flickering light produced by the rotation of a potters wheel could reveal a type of epilepsy.
Although there does not appear to be any scientific research suggesting auditory entrainment can cause a seizure if you are prone to them or are pregnant (in case you are prone to seizures and are not aware of it) it is recommend that you consult a doctor or medical professional before listening.