To reject votes, a concurrent resolution of both Houses is needed. That is not correct. There is no resolution, concurrent or otherwise, for that purpose.
In fact, the joint meeting for the purpose of counting electoral votes has been held under a concurrent resolution since, at least, 1888. The text of the concurrent resolution for the 2017 joint meeting is provided in my answer to What procedures are in place to stop a U.S. Vice President from ignoring electors?. Were the president allowed to veto the concurrent resolution for the joint meeting, the meeting could be postponed until January 20th or later.
That approval by the president is not required for concurrent resolutions is explained in the emboldened text below.
Article I, Section 7, Clause 3: Passage of Orders, Resolutions, or Votes
Every Order, Resolution, or Vote to which the Concurrence of the Senate and House of Representatives may be necessary (except on a question of Adjournment) shall be presented to the President of the United States; ...
Presentation of Resolutions
The purpose of clause 3, the Orders, Resolutions, and Votes Clause (ORV Clause), is not readily apparent. For years it was assumed that the Framers inserted the clause to prevent Congress from evading the veto clause by designating as something other than a bill measures intended to take effect as laws. Why a separate clause was needed for this purpose has not been explained. Recent scholarship presents a different possible explanation for the ORV Clause—that it was designed to authorize delegation of lawmaking power to a single House, subject to presentment, veto, and possible two-House veto override. If construed literally, the clause could have bogged down the intermediate stages of the legislative process, and Congress made practical adjustments. At the request of the Senate, the Judiciary Committee in 1897 published a comprehensive report detailing how the clause had been interpreted over the years. Briefly, it was shown that the word "necessary" in the clause had come to refer to the necessity for law-making; that is, any "order, resolution, or vote" must be submitted if it is to have the force of law. But "votes" taken in either House preliminary to the final passage of legislation need not be submitted to the other House or to the President, nor must concurrent resolutions merely expressing the views or "sense" of the Congress.