According to a recent statement from Nintendo to Nintendo Enthusiast, players will have a way to combat inappropriate content in Super Mario Maker levels.
According to the statement, there is not an automatic profanity filter for Super Mario Maker levels; any level can be created and uploaded, provided that the creator can beat the level. However, players can report inappropriate content, which will then be reviewed by Nintendo moderators. These moderators will make a decision to take the level down or leave it up; it’s currently unknown if there will be any additional penalty for creating obscene levels.
Source: Nintendo Enthusiast