Is it permissible to earn money or credit from applications that contain prohibited and beneficial content, by only watching the beneficial content and sending the application to others without guaranteeing what they will watch?

If the questioner does not know how people use the application, and whether they limit themselves to what is permissible, then he must act based on his predominant assumption about them. Otherwise, he should act based on the prevalent way people use the application, if he knows it. If there is no prevalent use, the default is permissibility.