Liberty Fund has a cheap edition of the Pacificus-Helvidius Debates. There, Hamilton and Madison agree that this right of the president isn’t anything more than ceremonial.
In general, Congress has the right to hear from anyone it wants. It can subpoena anyone it wants. It isn’t for the Executive Branch to have any role in such matters. In fact, more than one president has testified before Congress.
The bottom line is that the invitation to give the speech in itself didn’t violate any provision of the Constitution.
