If by "cover traffic" you mean there are other users on the system then you are correct. If by "cover traffic" you mean internally generated traffic that can be used to obscure traffic between any two links (e.g. keep a fixed size bandwidth pipe full even when not in use) then you are incorrect. The former is of little value in thwarting traffic analysis and the latter is costly in terms of already limited system performance and imposes costs on participants that few are willing to bear.
