I'm not sure why you are being downvoted, you are correct. If the normal state of the dam is to generate electricity then the obvious response to excess supply is to stop the flow. No need to pump anything back uphill unless the excess exceeds the normal capacity of the dam.
> If the normal state of the dam is to generate electricity
It isn't, at least not in the sense that you likely mean.
That seems to be a common misconception about the Hoover Dam. Its ability to generate electricity is completely secondary to its primary purpose: controlling the flow of water (e.g. flood control, irrigation).
Unless/until there is a lower reservoir (as proposed by the project in the article) that takes over that primary function, changing the flow through the dam for any electricity-related reasons is simply not an option.
