"Generally the term ought is used to denote blameworthiness"
Why do you say this? That's not at all how the term is commonly used! Both in the philosophical literature and in everyday conversations "You ought to do X" is usually used in the sense of "You have a moral obligation to do X". In that sense utilitarianism seems indeed incompatible with ought implies can, because classical utilitarians believe that you can have obligations which you cannot fullfil.
You are correct that we can use words however we want, but the utilitarian should at least admit that this would be a complete re-definition of the word "ought".
"Generally the term ought is used to denote blameworthiness"
Why do you say this? That's not at all how the term is commonly used! Both in the philosophical literature and in everyday conversations "You ought to do X" is usually used in the sense of "You have a moral obligation to do X". In that sense utilitarianism seems indeed incompatible with ought implies can, because classical utilitarians believe that you can have obligations which you cannot fullfil.
You are correct that we can use words however we want, but the utilitarian should at least admit that this would be a complete re-definition of the word "ought".