Possible Rationale
In Hollingsworth v. Virginia, the United States Supreme Court offered no rationale for its holding. Although the Court held that a presidential signature was not necessary for valid ratification, that holding is limited to the precise facts that were actually before the Court. The Court may have taken the position – as is likely – that the President has no constitutional power to sign, veto or pocket veto congressionally proposed amendments. But the Supreme Court nowhere expressed this position in its Hollingsworth opinion. Other rationales for Hollingsworth are also possible. For example, the Court may have taken the position that once ratified by the requisite number of States, an amendment or proposed amendment can no longer be challenged. The logic here is that "ratification" cures "defects". Alternatively, the rationale for Hollingsworth may have been that a Presidential proclamation of ratification is conclusive upon the courts notwithstanding arguable defects in the ratification process. See Luther v. Borden (1849). More importantly, in Hollingsworth, the proposed amendment was delivered to the President more than ten days prior to Congress's end of session adjournment. Under these circumstances, the absence of a presidential signature does not work a veto, but implies assent under the procedures laid out in Article I, even assuming they apply to the amendment process of Article V.
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