It is not a big surprise that Samsung uses IMX sensor from Sony on its latest flagships that are available on some markets. A Korean company also installs sensors, produced on their semiconductor division. IMX and Samsungs sensors have the same specifications in order to guarantee equally perfect quality of photos and Slow Motion videos. (Super Slow Motion feature allows making around 950 frames per one second)
Camera sensors on Galaxy S9 are different on various markets
Sensor IMX from Sony is almost the same as one that is used in Xperia XZs. It is a first device that made it possible to record slow mo videos with the speed more than 950 frames a second. Samsung uses camera sensors in Galaxy S9 that are better than sensors used in the previous flagship. Samsung continues underlying that its sensor is really unique and can guarantee a perfect noise free picture even in bad light conditions. Sensor from Sony is also of a highest quality, so you will not be able to mention difference between them. Both sensors are used in a rare camera.
There is no definite info about sensors used in front cameras of Galaxy S9. In reality, there is no difference if Samsung uses own ones or from Sony. It only means that Samsung needs Sony’s help in producing millions of fresh Smartphones that are sold all over the world.