Yes, if an historian is cited as a source, then by definition he personally is a secondary source. History is based on a preponderance of the evidence, not unlike a legal investigation. The evidence may come from primary and secondary sources. The trick is to evaluate the sources. Primary source material, as we all know, is not always reliable. Take for example, Julius Caesar's "Commentaries on the Gallic Wars" or John Bell Hood's "Advance and Retreat." Both of these primary sources (primary being defined in this case as the writings of someone who had "been there, done that") are heavily agenda-driven and self-serving. It is appropriate to use and cite them in one's research; indeed, I would question the accuracy any history which did not do so, since as primary sources they are a part of the context of the historial event being written about. However, any historian worthy of the title would certainly evaluate his primary sources as to their accuracy and motives, and shape his historical treatise accordingly.
Likewise, secondary sources must be evaluated as their accuracy and motives, as well as their qualifications and reputations. It doesn't matter whether the treatise was written by Douglas Southall Freeman, Bruce Catton, or Miss Ballard's third-grade class. Unless or until time travel becomes a reality, we can only rely on the preponderance of the evidence as presented by historians whose experience, motives and writings can stand up to scrutiny. It ain't perfect, but it's all we've got.
As one American president commented on the eve of a nuclear arms discussion with the Soviets, "Trust, but verify."