Is it permissible to inform the website owner about the problems with his site – which is rife with obscenity – in order to improve it, and would that be considered an encouragement for such sites to improve?

It is impermissible to support websites that are rife with indecency, or to cause their improvement or promotion, because "the means take the ruling of their ends," and due to the Almighty's saying: "And do not cooperate in sin and aggression." Therefore, it is not permissible to inform the owners of these websites about their problems for the purpose of improving them, even if no solutions are provided to them, because that is considered a means of rectifying them and assisting in their forbidden work.