IANAL, but I suspect they would not own copyright on a scan of a public domain work, at least not in the U.S., because of the precedent set down in Bridgeman v. Corel. Corel distributed non-original photographs taken by Bridgeman Art of public domain art works, and Bridgeman sued them, claiming they owned the copyright to those images. According to the decision, because the photographs were slavish copies of public domain works, the photographs themselves had no original element and thus couldn't be copyrighted.
as Wikipedia puts it:
"Bridgeman Art Library v. Corel Corp., 36 F. Supp. 2d 191 (S.D.N.Y. 1999), was a decision by the United States District Court for the Southern District of New York, which ruled that exact photographic copies of public domain images could not be protected by copyright because the copies lack originality. Even if accurate reproductions require a great deal of skill, experience and effort, the key element for copyrightability under U.S. law is that copyrighted material must show sufficient originality."